In computer keyboards, the enter key (or the return key) in most cases causes a command line, window form or dialog box to operate its default function, which is typically to finish an "entry" and begin the desired process.
The return key is often also referred to as (and even marked as) the enter key and it usually performs the same function as the enter key, but in some applications (mainly page layout, word processing and in typewriting) it's the one that operates like the carriage return key from which it originates. It typically has an arrow pointing down and left, which is the symbol for carriage return.
The enter key is typically located on the lower right of the numeric keyboard, and the return key (often marked as the enter key) on the right edge of the keyboard, under backspace.
In pocket calculator-like programs (for example, Microsoft Windows Calculator), the enter key of the numeric keypad acts like the equal to (=) button to obtain the result of the previously entered operations.
Usually the default button on a form is highlighted, giving a subtle visual clue that the user has the option of clicking the button or simply pressing Enter.
In modern word processing applications, pressing the enter key ends a paragraph and starts a new one. Spacing between the paragraphs can be defined through paragraph styles. Some people, however, tend to use the enter key twice or more times to space paragraphs apart. On the contrary, using the enter key to space paragraphs in plain text files is normal.
On some keyboard layouts, the Return and Enter key are two different keys, an artifact of the differing handling of newlines by different operating systems. As an example, on the Macintosh, the Return key is the usual key, while the Enter key is positioned at the lower right of the numeric key pad. For example, while using the text tool in Adobe Photoshop, the Return key produces a new line while the Enter key ends editing mode; Apple also took advantage of this situation to create a highly editable command line environment called a "Worksheet" in the Macintosh Programmer's Workshop, where Return was used strictly as a formatting key while Enter was used to execute a shell command or series of commands in direct mode. (In technical terms, the Macintosh keyboard maps the Return key to a carriage return, while the Enter key maps to a line feed.)