[iBook] Is this a crash?

[patdart]

Something just happened to me that has never happened before on my 
iBook.  I've used Macs since 1990 or earlier and this was a new 
experience.  I was reading email thru Mail and had Safari open and 
suddenly, as I attempted to open a new page, all the screens 
disappeared and a plain blue page was visible with nothing on it except 
the turning ball, and as I watched my desktop came up.  I did a restart 
and all seems okay now, but is this a "crash" and what should I do?  Do 
I have maintenance that I need to do?

This is on my iBook, running 10.2.8, in case that matters.

Pat