TITLE: What is a central projection?
QUESTION [6 upvotes]: What is a central projection in the context of a C*-algebra or a W*-algebra? Unfortunately while I see results on this concept, I haven't been able to find a definition.
Thanks!

REPLY [5 votes]: It is just a projection that is central (i.e., in the center).  That is, a central projection in a *-algebra $A$ is an element $p\in A$ such that $p=p^*$, $p^2=p$, and $px=xp$ for all $x\in A$.