a phone is bricked when it doesn't boot, doesn't turn on, WHEN YOU CAN'T ENTER IN RECOVERY (if you can is not bricked)...
there is an unbricking project in the development section that regards just one type of bricking....I don't know what is it exactly...
I just flash roms, this usually doesn't brick the phone...
you risk to brick when you try to change the hboot, when you try to s-on your s-off device...when you enter deeply in the system of your phone...
flashing kernel, roms, modding, rooting...these things doesn't brick nothing

so just do that if you are not a dev.
cheers