Glossary of oil and gas industry geophysical terms
Sheriff's Encyclopedic Dictionary is the closest thing to a canonical text, but the Schlumberger glossary is more up to date.

Sheriff is a scientific text, whereas the Schlumberger glossary is a little more generally accessible, but neither is comprehensive. Sheriff is especially poor on recent advances. On the plus side, you can edit it, if you're an SEG member.

After those two, Wikipedia is probably your next best bet.