An intersection is a single point where two lines meet or cross each other. In the figure above we would say that "point K is the intersection of line segments PQ and AB". Another way it may be said is that "the line segment PQ intersects AB at point K".
Note that two line segments need not necessarily intersect anywhere. In the figure above, adjust point B upwards until the two line segments no longer intersect. However, recall that lines (as opposed to line segments) go on forever in both directions, and so they will always intersect somewhere unless they are exactly parallel.