Rebasing is the process of creating a shared library image in such a way that it is guaranteed to use virtual memory without conflicting with any other shared libraries loadable in the system.
Some security extensions to Linux/x86 use rebasing to force the use of code addresses below 0x00ffffff in order to introduce a 0x00 byte into all code pointers; this eliminates a certain class of buffer overflow security problems related to improper checking of null-terminated strings, common in the C programming language.