Keyword Proximity

Keyword proximity refers to the closeness between two or more keywords. In general, the closer the keywords are, the better.

For example:

How Keyword Density Affects Search Engine Rankings

Using the example above, if someone searched for search engine rankings, a web page containing the first sentence is more likely to rank higher than the second.

The reason is because the keywords are placed closer together. This is assuming that everything else is equal, of course.