"Build" is a term with several meanings. You can infer the intended definition from the way it is used in each instance.
ArenaNet often announces in-game that "a new build of Guild Wars is available." This means that the game has been updated while you have been playing. You should quit the game and re-start to get the update.
 Character builds
A character build refers to the composition of a character. As there are a myriad of ways to develop a character, different builds are often compared, discussed, lauded and criticized in web forums and/or chat rooms.
For Guild Wars, the following information is usually pertinent:
- Primary profession
- Secondary profession
- Attributes used (including the amount of points alloted to each)
- Equipped skills
The following information is also occasionally included:
Also, while not being an essential part of a build, a strategy description often helps other players to better understand a build's purpose, strengths, and weaknesses.
 Team builds
A team build refers to the combination of individual character builds to form a party. A team build should include the needed individual builds as well as strategy for how the players should work together.
 Builds on PvXwiki
A list of builds can be found here, organized into subcategories.
The subcategories contain builds that have been created and tested by users of this wiki. Some will work well for you, some might not. Always remember that everyone should play with the build they are most comfortable with and do not hesitate to tweak any build you see to your specific needs. These are rather starting points for your own build than "set-in-stone" final wisdom.
If you're feeling adventurous, or just want more inspiration, you may also wish to have a look at the not-so-complete untested builds. You could even test some of them out and help improve them.
To add your own build to the Wiki, please visit PvXwiki:Writing good builds and make sure your build meets the page's criteria. After that, visit PvXwiki:Style and formatting for instructions on how to create a build article.