Compile All the source files in the specified scope are compiled. The scope in this case may be a file, a package, etc.
Make Project All the source files in the entire project that have been modified since the last compilation are compiled. Dependent source files, if appropriate, are also compiled. Additionally, the tasks tied to the compilation or make process on modified sources are performed. For example, EJB validation is performed if the corresponding option is enabled on the Validation page.
Make Module Compiled are all the source files that have been modified since the last compilation in the selected module as well as in all the modules it depends on recursively.
Rebuild Project All the source files in the project are recompiled. This may be necessary when the classpath entries have changed, for example, SDKs or libraries being used added, removed or altered