"Reset" is one of three possible button types in HTML 4.0 which can be placed in an HTML form (the other two being "submit" and the non-functional "button"). You specify it using something like the following code:
<INPUT TYPE="reset" VALUE="Clear the form">
Okay now, here's the thing: DON'T EVER USE THIS. I mean it. There is almost never any reason for an end user of your HTML forms to want to clear the form. However, since a reset button looks just like a submit button, a user can easily click on it instead by not reading or by aiming their mouse badly. And the longer the form, the more annoying this sort of accident is, and the more likely the user is to not bother filling the form out a second time.
Besides, when was the last time you were filling out a form online and thought, "Hey, I'd better clear all those fields just in case I click on that 'submit' button without meaning to"?
Notice that nate doesn't use reset buttons. You shouldn't either. Be like nate.