A build option is a recommended way to build a 1st level character in a certain class. The class was constructed with these options in mind, and its powers, features, skills etc are meant to cater to one or more of these choices.

However, a player is not required to use the build options given. A player can mix between them (grabbing some things that work well for one and some that work well for another), or even take the class in a completely different direction that may not have been foreseen by its designers. Build options are simply recommendations.