What is the difference between blacklisted, bad imei and activation lock?

I want to know the difference between these term - blacklisted, bad imei and activation lock

and for a iphone should i buy any phone that is blacklisted, bad imei or activation lock

is it possible to bypass it… In the past i have bypass sim activation so is this possible as well?

Blacklisted, Bad IMEI or Bad ESN mean that the phone has been reported lost or stolen and can't be used as a cell phone again. These phones are generally sold to be striped of workable parts like the case and screen for a phone that is currently working but in disrepair.

Activation lock means that a phone was stolen and can't be activated because it was never processed to be activated.

No, you can't activate any phone that has any of these issues.