Question

two planes intersect in a what?

Answer 1

Imagine it in your head; or take two pieces of paper/cardboard -- what does it look like?

Their intersection looks like a straight line.

Answer 2

in a crash ;)

Answer 3

(unless of course the planes are equal in which case their intersection is themselves)

Answer 4

so idk wat it is

Answer 5

Read JamesJ's answer until you understand it. The answer is there.