Stupid question!

I'm all new to this forum stuff and I just wanted to know:

What is the difference between a thread and a topic?

On the Internet in Usenet newsgroups and similar forums, a thread is a sequence of responses to an initial message posting. This enables you to follow or join an individual discussion in a newsgroup from among the many that may be there. A thread is usually shown graphically as an inital message and successive messages "hung off" the original message. As a newsgroup user, you contribute to a thread by specifying a "Reference" topic as part of your message.

Cools, i get it now. Thanks!