The computer industry has adapted the concept of a
Style Guide from the print industry.
(one of the books on style is
The Elements of Style, William Strunk, Jr. [http://www.bartleby.com/141]published in 1918).
In the print industry this is a guide that describes
standard ways of writing things so that they
appear to be written by one person and are consistent
(when describing two things that are similar, the language is identical or nearly identical) .
For example Sports Illustrated uses a different Style Guide
than Cosmopolitan, yet each magazine has a consistent look and writing style.
Specifically in a publication like People magazine the
"Picks & Pans" section has reviews.
Each page has the type of review (tube, screen, song, or pages) in a bar on the page.
The bar for each type of review has a different background color corresponding to the type of review.
For example all of the screen reviews have a purple background.
The text is all written in third person present tense active voice
("there are" versus "there were," "I am," or "I was").
A style guide for software describes the layout and behavior of the software: colors
of various graphical elements, layout of text, what happens when the user
pushed certain keys or enters certain data.
Note that describing what happens is in general terms: "when
the user pushes the insert key, the cursor will change to a
solid box and when the user types, the next character will
be inserted to the right of the cursor and the cursor will
then be moved on top of the just inserted character." Or
"When the user enters a General Ledger Account Number, the
software will check the General Ledger to make sure the Account Number exists."