Bootstrap refers to the loop of leather that helps to pull a boot over your foot.
It's similiar to booting I guess:
[Wikipedia] http://en.wikipedia.org/wiki/Bootstrapping#Applications -
"Booting is the process of starting a computer, specifically in regards to starting its software. The process involves a chain of stages, in which at each stage a smaller simpler program loads and then executes the larger more complicated program of the next stage. It is in this sense that the computer "pulls itself up by its bootstraps""
The Composite Application Library has an implementation for initialisation but I have seen other proprietary implementations e.g. pulling down applications to compute grid nodes and launching them.
I suppose ClickOnce could also be thought of as a bootstrapper when lanuching applications.