<s>
MEAN	O
(	O
MongoDB	B-Application
,	O
Express.js	B-Language
,	O
AngularJS	B-Application
(	O
or	O
Angular	B-Language
)	O
,	O
and	O
Node.js	B-Language
)	O
is	O
a	O
free	B-License
and	I-License
open-source	I-License
JavaScript	B-Language
software	B-Application
stack	I-Application
for	O
building	O
dynamic	O
web	O
sites	O
and	O
web	B-Application
applications	I-Application
.	O
</s>
<s>
A	O
variation	O
known	O
as	O
MERN	O
replaces	O
Angular	B-Language
with	O
React	B-Application
.	O
</s>
<s>
Because	O
all	O
components	O
of	O
the	O
MEAN	B-Application
stack	I-Application
support	O
programs	O
that	O
are	O
written	O
in	O
JavaScript	B-Language
,	O
MEAN	O
applications	O
can	O
be	O
written	O
in	O
one	O
language	O
for	O
both	O
server-side	B-Application
and	O
client-side	B-Operating_System
execution	O
environments	O
.	O
</s>
<s>
Though	O
often	O
compared	O
directly	O
to	O
other	O
popular	O
web	O
development	O
stacks	O
such	O
as	O
the	O
LAMP	B-Application
stack	I-Application
,	O
the	O
components	O
of	O
the	O
MEAN	B-Application
stack	I-Application
are	O
higher-level	O
including	O
a	O
web	B-Application
application	I-Application
presentation	O
layer	O
and	O
not	O
including	O
an	O
operating	O
system	O
layer	O
.	O
</s>
<s>
He	O
introduced	O
the	O
term	O
in	O
a	O
2013	O
blog	O
post	O
and	O
the	O
logo	O
concept	O
,	O
initially	O
created	O
by	O
Austin	O
Anderson	O
for	O
the	O
original	O
MEAN	B-Application
stack	I-Application
LinkedIn	B-Application
group	O
,	O
is	O
an	O
assembly	O
of	O
the	O
first	O
letter	O
of	O
each	O
component	O
of	O
the	O
MEAN	O
acronym	O
.	O
</s>
<s>
MongoDB	B-Application
is	O
a	O
NoSQL	O
database	O
program	O
that	O
uses	O
JSON-like	O
BSON	B-Protocol
(	O
binary	B-Protocol
JSON	I-Protocol
)	O
documents	O
with	O
schema	O
.	O
</s>
<s>
The	O
role	O
of	O
the	O
database	O
in	O
the	O
MEAN	B-Application
stack	I-Application
is	O
very	O
commonly	O
filled	O
by	O
MongoDB	B-Application
because	O
its	O
use	O
of	O
JSON-like	O
documents	O
for	O
interacting	O
with	O
data	O
as	O
opposed	O
to	O
the	O
row/column	O
model	O
allows	O
it	O
to	O
integrate	O
well	O
with	O
the	O
other	O
(	O
JavaScript-based	O
)	O
components	O
of	O
the	O
stack	O
.	O
</s>
<s>
Express.js	B-Language
(	O
also	O
referred	O
to	O
as	O
Express	O
)	O
is	O
a	O
modular	O
web	B-Application
application	I-Application
framework	O
package	O
for	O
Node.js	B-Language
.	O
</s>
<s>
While	O
Express	O
is	O
capable	O
of	O
acting	O
as	O
an	O
internet-facing	O
web	O
server	O
,	O
even	O
supporting	O
SSL/TLS	O
out	O
of	O
the	O
box	O
,	O
it	O
is	O
often	O
used	O
in	O
conjunction	O
with	O
a	O
reverse	B-General_Concept
proxy	I-General_Concept
such	O
as	O
NGINX	B-Operating_System
or	O
Apache	B-Application
for	O
performance	O
reasons	O
.	O
</s>
<s>
Typically	O
data	O
is	O
fetched	O
using	O
Ajax	B-General_Concept
techniques	O
and	O
rendered	O
in	O
the	O
browser	O
on	O
the	O
client-side	B-Operating_System
by	O
a	O
client-side	B-Operating_System
application	O
framework	O
,	O
however	O
as	O
the	O
stack	O
is	O
commonly	O
entirely	O
JavaScript-based	O
,	O
in	O
some	O
implementations	O
of	O
the	O
stack	O
,	O
server-side	B-Application
rendering	O
where	O
the	O
rendering	O
of	O
the	O
initial	O
page	O
can	O
be	O
offloaded	O
to	O
a	O
server	O
is	O
used	O
so	O
that	O
the	O
initial	O
data	O
can	O
be	O
prefetched	O
before	O
it	O
is	O
loaded	O
in	O
the	O
user	O
's	O
browser	O
.	O
</s>
<s>
Node.js	B-Language
is	O
the	O
application	O
runtime	O
that	O
the	O
MEAN	B-Application
stack	I-Application
runs	O
on	O
.	O
</s>
<s>
The	O
use	O
of	O
Node.js	B-Language
,	O
which	O
is	O
said	O
to	O
represent	O
a	O
"	O
JavaScript	B-Language
Everywhere	O
"	O
paradigm	O
,	O
is	O
integral	O
to	O
the	O
MEAN	B-Application
stack	I-Application
which	O
relies	O
on	O
that	O
concept	O
.	O
</s>
