Boost.Build is the name of the complete build system. The executable that runs it is b2. That executable is written in C and implements performance-critical algorithms, like traversal of dependency graph and executing commands. It also implements an interpreted language used to implement the rest of Boost.Build. This executable is formally called "Boost.Build engine".

The Boost.Build engine is derived from an earlier build tool called Perforce Jam. Originally, there were just minor changes, and the filename was bjam. Later on, with more and more changes, the similarity of names because a disservice to users, and as of Boost 1.47.0, the official name of the executable was changed to b2. A copy named bjam is still created for compatibility, but you are encouraged to use the new name in all cases.

Perforce Jam was an important foundation, and we gratefully acknowledge its influence, but for users today, these tools share only some basics of the interpreted language.