Somewhat new to coaching. Could you tell me what the terms over and under correspond to?

Over and under is when the d line mainly the inside player shift either to the strong or weak side of the defense. The over might be what you call your normal d alignment, while the under side of it is that the two tackles switch shades. for example the strong side tackle who might line up on the outside of the strong gaurd, and the weak tackle who lines up inside of the gaurd, but in the under the strong tackle move in side the gaurd and the weak tackle moves to the oustide shade on the weak gaurd. Most coaches might do something different, this is how we do it in a 40 front, the 50 front the ends are also involved in the movement. Sometimes coaches move their strong end inside (under) the TE. Hope this helps.
0 0 0 x 0 0
e t t e

0 0 0 x 0 0
e t t e