Let's talk cursors. Actually, it's the old-timers who say "cursors" while everyone else calls them "pointers." Apple uses both terms interchangeably in their documentation (yes, Apple does provide documentation, which can be found at support.apple.com).
Pointers are the endearing little on-screen indicators designed to provide feedback to users. According to the latest revision of Apple's Human Interface Guidelines document, there are eighteen system pointers in OS X.
A few of the typical OS X system pointers
The two system pointers we're most familiar with are the "mouse pointer" – "arrow" is it's official moniker – and the “I-beam." The latter is used to indicate the text insertion point wherever you need to... you know… insert text. And then, there is the dreaded "Spinning Pizza of Death.” Well, that’s what I call it, anyway.
The Spinning Wait Cursor (that's Apple's terminology
For the sake of accuracy, let's call it what Apple deems to be the official name: the "Spinning Wait Cursor." On second thought, "Spinning Pizza of Death" is more fun. And tasty, too, come to think of it. You don't want to see this one often. The details as to why we see it on occasion, as well as how to avoid it, are subjects reserved for future discussion. Suffice it to say that you want to minimize the appearance of this pirouetting pinwheel, which basically indicates that OS X is commandeering the system for its own needs and may be a harbinger of serious system maintenance.
Next: Resizing the Pointer