When two straight lines meet or cross each other, they form __________.

When two straight lines meet or cross each other, they create an angle at the point where they intersect. Angles are formed by the two rays that emanate from the intersection point, with each ray being part of one of the lines. The space between these two rays is what we define as an angle, which can vary in measurement depending on how the lines intersect.

In geometry, while lines may also be classified as parallel, tangential, or perpendicular based on their relationships and orientations, the act of simply crossing or meeting is what distinctly forms an angle. This makes the concept of an angle fundamental when discussing intersections of lines.

Parallel lines, for instance, do not meet or cross at any point, while tangential lines meet at a single point but don’t form an angle in the traditional sense of intersecting lines. Perpendicular lines specifically intersect at a right angle (90 degrees), which is a more specific case of the general scenario where any two lines intersect and form angles. Thus, the creation of an angle is the most inclusive and accurate description of the action that occurs when two straight lines cross each other.