The rate at which energy is absorbed by the body when exposed to RF is referred to as the specific absorption rate, or SAR.

FORBES: Should The FCC Re-Examine Cell Phone Radiation?

The Federal Communications Commission limits cell phone radio frequency energy emissions, called the specific absorption rate (SAR), at 1.6 watts per kilogram, as measured over one gram of tissue.

CNN: Scientists debate possible cell phone link to brain cancer

The Australian research focused on the thermal effects or specific absorption rate (SAR) of radio frequency radiation - a measure of its actual effects on brain tissue, whereas the earlier study simply looked at electromagnetic radiation levels.

BBC: Hands-free mobiles given safety boost