HVT, LVT

http://www.edaboard.com/thread135577.html

HVT - High V threshold. Can be used in the path where timing is not critical. So by using HVT cells we can save power.
LVT - Low V threshold. One should use these cells in timing critical paths. These cells are fast but , comsumes more power due to its leakage. So it will consume more power. So use only when timing is critical.
SVT - Standard V threshold. Best of both world. Medium delay and medium power requirment. So if timing is not met by small magin with HVT, you should try with SVT. And at last LVT.