What does each letter in the formula stand for? What does each item stand for?

Then combined with image understanding, understand the content expressed by the formula.

The relationship between a straight line and a plane is three, parallel, intersecting and on the plane. You have to understand the relationship between these three positions. You regard the plane as a line. Just like two lines, their positional relationship is only two, intersecting and parallel, don't you think so? In fact, the straight line and the plane intersect parallel, on the plane, that is, the two lines overlap! . Understand this meaning, which axioms are not immediately understood.