what is a straight edge

Question

a sraight line is a line that has a one end point and a arrow that keeps going the other direction

Answer 1

It is a means of drawing a straight line, but without the ability to measure distances along the line.

Answer 2

It looks like you may have answered your own question. In practical, useful every-day terms, a straight edge is anything with a hard, stright-line edge, which we normally use to mark or cut a straignt line in some material (wood, cloth, etc.).  An example is the edge of any normal school measuring ruler.