what is a "global"

Hi, I thought i knew the useage of the "global" keyword in a function but after reading a pals program i am really confused, i tried http://php.net/global but that does not give me any results...searched the list and found some reference to global and the "scope" of the function but still confused. Anybody have a good link or can give me a place to read up on the defination with an example? Thanks, -Ryan