Ramming = crashing into enemies at full speed.
Your Corvette's best weapon is the 1600T of mass hitting the enemy at 250+ m/s. It can do 4000 RAW damage that completely ignores shield resistances, too.
4:1:1 means 4 pips to SYS, 1 pip to ENG, and 1 pip to WEP. Having 4 pips in SYS means that you only take 40% of the damage when you ram something.
In a head-on crash between two ships, the damage is based on mass so in a huge Corvette you do LOADS of damage to other ships and they do much less damage to you in return. Of the big ships, Anacondas are light and worth ramming, but Cutters, other Corvettes, T-9 and T-10 are best to avoid. You'll do lots of damage to them but you'll lose a lot of your shields too.
Edit: I'm too slow, wrmiller got here before me! o7