An operation in a version control system or a special way of creating a shared library. (In order of the question counts in Stack Overflow)
Version Control Systems
In some source control system (also known as Version Control Systems o vcs) that support branches a
rebase is one of the ways of integrating the changes of one branch into another by changing the "father" or starting point of a branch.
Support it's still in an early status (March 2013)
Creating a shared library to avoid conflicts with other libraries in the usage of virtual memory. (Wikipedia)