Very naive question...
 

There must be a name for the socket on the bottom of a camera/camcorder to allow it to be fixed to a tripod, but I don't know what it is.

I've got a Sony DCR-TRV110e camcorder and it's been used with a Manfrotto tripod for years and years. Way back when, I had to buy a separate "mounting plate" to sit between the tripod and camcorder. Upon upgrading to the XL2 will I have to buy a new plate or does it have the same sized socket as the TRV110e?

I'm asking here because this information doesn't seem to be in any of the spec sheets for the XL2.

If you mean what I call the tripod plate screw hole, it should be
'quarter twenty.' 1/4" hole with 20 thread pitch. This is the most
common screw made.

Here is a link to the picture of the XL2 showing where the tripod mounting is located http://www.dvinfo.net/canonxl2/images/images06.php
As the picture caption states, that is for a TA-100 Tripod adapter that can be connected to the camera body. Hope this helps.