&ltbt&gt

I was wondering if someone could please explain to me all the different <t>'s that there are. I know that <t> means "target" and that <bt> means "battle target"...but I think that I have heard of other ones, and I'm confused to what they all mean and when one should be used over another. Which...

Which do you prefer? I think of <bt> as "The Targeting command that won't get your entire party killed" while <t> is "trouble if you get mixed up."