From Unofficial BOINC Wiki
A term we apply to a computer that is used by an individual and is usually slower, less complex, and less expensive that computers that are used by organizations to do work. Computers that are readily available in stores are all (well, almost always) Personal Computers.
Computers that might have internal architectures similar to a PC but are generally faster and have more memory are called "Servers" and these Servers may be used to Host the following BOINC System componentss:
It is possible that a person may have a computer of significantly greater capacity, speed, complexity, and cost than a typical PC, but this is usually only a condition suffered by Crunchers and other weirdos like me.