Bootstrapping is the process of implementing a virtual machine by implementing it using an existing virtual machine. So, for example perl 5, CPython, ruby, php and the Tcl interpreter are all written in C. That way they can be bootstrapped to run on any system for which a C compiler (such as the Open-Source gcc is available).
A related concept is Self-hosting, where a virtual machine's compiler or interpreter is written in itself. So for example, gcc is written in C and requires a C compiler to be built.
For C it is not really a problem, because one can use gcc or a different C compiler to cross-compile enough programs for it to run there conveniently. However,