Trying to clarify exactly what is meant by "burning" SBD !!

This is a direct point that it needs real specialist here on steemit to reply and give the real information.

For another direction, If you exchange it in the market for steem, is that burning it or does it merely put it on the market? Also, does powering up burn steem?

Well, the answer is came out by Mr. Mini Smallholding @minismallholding in his blog/post of source :
https://steemit.com/steem/@minismallholding/minismallholding-re-felixxx-sbd-conversion-20190204t123656744z

as per the followings :

1-If you exchange your SBD in the market, someone else gets them.

2-When you power up STEEM you take it off the market, but they are not really 'burned' since you can power back down.

3-When you send them to @null or convert them via the wallet function, you actually destroy those SBD.

I hope this will help you to understand more the terminology here in steemit of "burning" SBD !!