Caesura is a fancy word for a not-so-awkward pause that occurs in the middle of a line of verse in poetry. You can use this term if you want to sound smart, but we think "pause" is just fine.
You can create pauses in a lot of ways, but the most obvious is to use punctuation like a period, comma, or semicolon. So if you see one of those smack dab in the middle of a line of poetry, chances are you're looking at a caesura. (Note that a pause at the end of a line is not a caesura.)
Caesurae were all the rage back in the good old days of Anglo-Saxon (or Old English) poetry. We're looking at you, Beowulf. The Anglo-Saxons were fond of caesurae because all those pauses added rhythm that helped them remember the poem itself, which was probably being recited all fancy-like at a banquet in a Mead Hall.