<s>
In	O
computing	O
,	O
a	O
plug-in	B-Application
(	O
or	O
plugin	B-Application
,	O
add-in	B-Application
,	O
addin	B-Application
,	O
add-on	O
,	O
or	O
addon	O
)	O
is	O
a	O
software	O
component	O
that	O
adds	O
a	O
specific	O
feature	O
to	O
an	O
existing	O
computer	B-Application
program	I-Application
.	O
</s>
<s>
When	O
a	O
program	O
supports	O
plug-ins	B-Application
,	O
it	O
enables	O
customization	O
.	O
</s>
<s>
A	O
theme	B-Application
or	O
skin	B-Application
is	O
a	O
preset	O
package	O
containing	O
additional	O
or	O
changed	O
graphical	O
appearance	O
details	O
,	O
achieved	O
by	O
the	O
use	O
of	O
a	O
graphical	O
user	O
interface	O
(	O
GUI	O
)	O
that	O
can	O
be	O
applied	O
to	O
specific	O
software	O
and	O
websites	O
to	O
suit	O
the	O
purpose	O
,	O
topic	O
,	O
or	O
tastes	O
of	O
different	O
users	O
to	O
customize	O
the	O
look	O
and	O
feel	O
of	O
a	O
piece	O
of	O
computer	O
software	O
or	O
an	O
operating	B-General_Concept
system	I-General_Concept
front-end	O
GUI	O
(	O
and	O
window	B-Application
managers	I-Application
)	O
.	O
</s>
<s>
Applications	O
may	O
support	O
plug-ins	B-Application
to	O
:	O
</s>
<s>
separate	O
source	O
code	O
from	O
an	O
application	O
because	O
of	O
incompatible	O
software	B-License
licenses	I-License
.	O
</s>
<s>
Types	O
of	O
applications	O
and	O
why	O
they	O
use	O
plug-ins	B-Application
:	O
</s>
<s>
Digital	B-General_Concept
audio	I-General_Concept
workstations	I-General_Concept
and	O
audio	B-Application
editing	I-Application
software	I-Application
use	O
audio	B-Application
plug-ins	I-Application
to	O
generate	O
,	O
process	O
or	O
analyze	O
sound	O
.	O
</s>
<s>
Ardour	B-Language
,	O
Audacity	B-Language
,	O
Cubase	B-Application
,	O
FL	B-Application
Studio	I-Application
,	O
Logic	B-Application
Pro	I-Application
X	I-Application
and	O
Pro	B-Application
Tools	I-Application
are	O
examples	O
of	O
such	O
systems	O
.	O
</s>
<s>
Email	B-Protocol
clients	I-Protocol
use	O
plug-ins	B-Application
to	O
decrypt	O
and	O
encrypt	O
email	O
.	O
</s>
<s>
Pretty	B-Application
Good	I-Application
Privacy	I-Application
is	O
an	O
example	O
of	O
such	O
plug-ins	B-Application
.	O
</s>
<s>
Video	O
game	O
console	O
emulators	O
often	O
use	O
plug-ins	B-Application
to	O
modularize	O
the	O
separate	O
subsystems	O
of	O
the	O
devices	O
they	O
seek	O
to	O
emulate	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
PCSX2	B-Application
emulator	O
makes	O
use	O
of	O
video	O
,	O
audio	O
,	O
optical	O
,	O
etc	O
.	O
</s>
<s>
plug-ins	B-Application
for	O
those	O
respective	O
components	O
of	O
the	O
PlayStation	B-Device
2	I-Device
.	O
</s>
<s>
Graphics	B-Application
software	I-Application
use	O
plug-ins	B-Application
to	O
support	O
file	O
formats	O
and	O
process	O
images	O
.	O
</s>
<s>
A	O
Photoshop	B-Operating_System
plug-in	I-Operating_System
may	O
do	O
this	O
.	O
</s>
<s>
Media	O
players	O
use	O
plug-ins	B-Application
to	O
support	O
file	O
formats	O
and	O
apply	O
filters	O
.	O
</s>
<s>
foobar2000	B-Application
,	O
GStreamer	B-Language
,	O
Quintessential	B-Application
,	O
VST	B-Application
,	O
Winamp	B-Application
,	O
XMMS	B-Language
are	O
examples	O
of	O
such	O
media	O
players	O
.	O
</s>
<s>
Packet	B-Protocol
sniffers	I-Protocol
use	O
plug-ins	B-Application
to	O
decode	O
packet	O
formats	O
.	O
</s>
<s>
OmniPeek	B-Protocol
is	O
an	O
example	O
of	O
such	O
packet	B-Protocol
sniffers	I-Protocol
.	O
</s>
<s>
Remote	B-Application
sensing	I-Application
applications	I-Application
use	O
plug-ins	B-Application
to	O
process	O
data	O
from	O
different	O
sensor	O
types	O
;	O
e.g.	O
,	O
Opticks	B-Algorithm
.	O
</s>
<s>
Text	B-Application
editors	I-Application
and	O
Integrated	B-Application
development	I-Application
environments	I-Application
use	O
plug-ins	B-Application
to	O
support	O
programming	O
languages	O
or	O
enhance	O
the	O
development	O
process	O
e.g.	O
,	O
Visual	B-Application
Studio	I-Application
,	O
RAD	O
Studio	O
,	O
Eclipse	B-Application
,	O
IntelliJ	B-Language
IDEA	I-Language
,	O
jEdit	B-Language
and	O
MonoDevelop	B-Language
support	O
plug-ins	B-Application
.	O
</s>
<s>
Visual	B-Application
Studio	I-Application
itself	O
can	O
be	O
plugged	O
into	O
other	O
applications	O
via	O
Visual	B-Application
Studio	I-Application
Tools	I-Application
for	I-Application
Office	I-Application
and	O
Visual	B-Application
Studio	I-Application
Tools	I-Application
for	I-Application
Applications	I-Application
.	O
</s>
<s>
Web	B-Application
browsers	I-Application
have	O
historically	O
used	O
executables	B-Application
as	O
plug-ins	B-Application
,	O
though	O
they	O
are	O
now	O
mostly	O
deprecated	B-General_Concept
.	O
</s>
<s>
Examples	O
include	O
the	O
Adobe	B-Operating_System
Flash	I-Operating_System
Player	I-Operating_System
,	O
a	O
Java	B-Language
virtual	I-Language
machine	I-Language
(	O
for	O
Java	B-Application
applets	I-Application
)	O
,	O
QuickTime	B-Application
,	O
Microsoft	B-Application
Silverlight	I-Application
and	O
the	O
Unity	O
Web	O
Player	O
.	O
</s>
<s>
(	O
Browser	B-Protocol
extensions	I-Protocol
,	O
which	O
are	O
a	O
separate	O
type	O
of	O
installable	O
module	O
,	O
are	O
still	O
widely	O
in	O
use	O
.	O
)	O
</s>
<s>
The	O
host	O
application	O
provides	O
services	O
which	O
the	O
plug-in	B-Application
can	O
use	O
,	O
including	O
a	O
way	O
for	O
plug-ins	B-Application
to	O
register	O
themselves	O
with	O
the	O
host	O
application	O
and	O
a	O
protocol	O
for	O
the	O
exchange	O
of	O
data	O
with	O
plug-ins	B-Application
.	O
</s>
<s>
Plug-ins	B-Application
depend	O
on	O
the	O
services	O
provided	O
by	O
the	O
host	O
application	O
and	O
do	O
not	O
usually	O
work	O
by	O
themselves	O
.	O
</s>
<s>
Conversely	O
,	O
the	O
host	O
application	O
operates	O
independently	O
of	O
the	O
plug-ins	B-Application
,	O
making	O
it	O
possible	O
for	O
end-users	O
to	O
add	O
and	O
update	O
plug-ins	B-Application
dynamically	O
without	O
needing	O
to	O
make	O
changes	O
to	O
the	O
host	O
application	O
.	O
</s>
<s>
Programmers	O
typically	O
implement	O
plug-ins	B-Application
as	O
shared	O
libraries	O
,	O
which	O
get	O
dynamically	B-Operating_System
loaded	I-Operating_System
at	O
run	O
time	O
.	O
</s>
<s>
HyperCard	B-Application
supported	O
a	O
similar	O
facility	O
,	O
but	O
more	O
commonly	O
included	O
the	O
plug-in	B-Application
code	O
in	O
the	O
HyperCard	B-Application
documents	O
(	O
called	O
stacks	O
)	O
themselves	O
.	O
</s>
<s>
Thus	O
the	O
HyperCard	B-Application
stack	I-Application
became	O
a	O
self-contained	O
application	O
in	O
its	O
own	O
right	O
,	O
distributable	O
as	O
a	O
single	O
entity	O
that	O
end-users	O
could	O
run	O
without	O
the	O
need	O
for	O
additional	O
installation-steps	O
.	O
</s>
<s>
Programs	O
may	O
also	O
implement	O
plug-ins	B-Application
by	O
loading	O
a	O
directory	O
of	O
simple	O
script	B-Language
files	O
written	O
in	O
a	O
scripting	B-Language
language	I-Language
like	O
Python	B-Language
or	O
Lua	B-Language
.	O
</s>
<s>
In	O
Mozilla	B-Operating_System
Foundation	I-Operating_System
definitions	O
,	O
the	O
words	O
"	O
add-on	O
"	O
,	O
"	O
extension	B-Protocol
"	O
and	O
"	O
plug-in	B-Application
"	O
are	O
not	O
synonyms	O
.	O
</s>
<s>
Mozilla	O
applications	O
come	O
with	O
integrated	O
add-on	O
managers	O
that	O
,	O
similar	O
to	O
package	B-Application
managers	I-Application
,	O
install	O
,	O
update	O
and	O
manage	O
extensions	O
.	O
</s>
<s>
The	O
term	O
,	O
"	O
plug-in	B-Application
"	O
,	O
however	O
,	O
strictly	O
refers	O
to	O
NPAPI-based	O
web	O
content	O
renderers	O
.	O
</s>
<s>
Mozilla	O
deprecated	B-General_Concept
plug-ins	B-Application
for	O
its	O
products	O
.	O
</s>
<s>
But	O
UXP-based	O
applications	O
,	O
like	O
web	B-Application
browsers	I-Application
Pale	O
Moon	O
and	O
Basilisk	O
,	O
keep	O
supporting	O
(	O
NPAPI	B-Protocol
)	O
plug-ins	B-Application
.	O
</s>
<s>
In	O
the	O
mid	O
1970s	O
,	O
the	O
EDT	B-Application
text	B-Application
editor	I-Application
ran	O
on	O
the	O
Unisys	O
VS/9	O
operating	B-General_Concept
system	I-General_Concept
using	O
the	O
UNIVAC	B-Device
Series	I-Device
90	I-Device
mainframe	B-Architecture
computer	I-Architecture
.	O
</s>
<s>
The	O
plug-in	B-Application
executable	B-Application
could	O
call	O
the	O
editor	O
to	O
inspect	O
and	O
change	O
the	O
text	O
.	O
</s>
<s>
The	O
University	O
of	O
Waterloo	O
Fortran	B-Application
compiler	O
used	O
this	O
to	O
allow	O
interactive	O
compilation	O
of	O
Fortran	B-Application
programs	O
.	O
</s>
<s>
Early	O
personal	O
computer	O
software	O
with	O
plug-in	B-Application
capability	O
included	O
HyperCard	B-Application
and	O
QuarkXPress	B-Operating_System
on	O
the	O
Apple	B-Device
Macintosh	I-Device
,	O
both	O
released	O
in	O
1987	O
.	O
</s>
<s>
In	O
1988	O
,	O
Silicon	O
Beach	O
Software	O
included	O
plug-in	B-Application
capability	O
in	O
Digital	B-Application
Darkroom	I-Application
and	O
SuperPaint	B-Application
.	O
</s>
