When we talk about tornado intensity you'll hear us use the EF scale, that means Enhanced Fujita scale.
Fujita is the gentleman that came up with the name for the scale to measure the intensity of tornadoes.
The weakest and most frequent is the EF0, this has winds of 65-85 mph. This will cause minor damage. Then we move to the EF1, this packs winds of 86-110 mph and this will cause moderate damage. Next we get into considerable damage with the EF2, this has winds of 111-135 mph. The scale goes up and so do the destructive winds. We're looking at the EF3. That has winds of 136 to 165 mph, causing severe damage. Then we move into the extreme category. This is the EF 4. This has winds of 166-200 mph.
Then finally, the most destructive of them all and the rarest is the EF5. Winds over 200 mph and this will cause total destruction.
The scale originally was called simply the "F" scale, but was changed to "EF".