# 4.4. Definitions

- Source tree: The tree where the Open MPI source code is located. It is typically the result of expanding an Open MPI distribution source code bundle, such as a tarball.

- Build tree: The tree where Open MPI was built. It is always related to a specific source tree, but may actually be a different tree (since Open MPI supports VPATH builds). Specifically, this is the tree where you invoked `configure`, `make`, etc. to build and install Open MPI.

- Installation tree: The tree where Open MPI was installed. It is typically the “prefix” argument given to Open MPI’s `configure` script; it is the directory from which you run installed Open MPI executables.