Beginning version 7, Vim started to introduce its auto-complete feature. By default it works by being able to auto-complete words that already existed in the file being edited. If enabled, it can also auto-complete syntax for various programming languages.
To use the Vim auto-complete feature, just hit
n while in insert mode, and you'll get a list of word suggestions as in the following example;
To make the list cycle backwards, hit
p. You can also use the arrow keys to move up and down the list.
To configure Vim to auto-complete programming language syntaxes (not just the already existing words in the document), follow any of the articles below.