Your question was also partially answered by this thread. A search would have revealed this.. The definition of Connection Pooling, of which a Google would have answered with the first hit being this..
Which would leave just the best practices, which I think would have been a good question :)
+1 to Keith's Answer. He has hit the nail right on the head.
Just a polite reminder from the FAQ:
You've searched the internet before asking your question, and you come to us armed with research and information about your question ... right?