Answer:
The amount of lines that are perpendicualr to the area and are closer together.
Step-by-step explanation:
Imagine a ripple of water. closer to the source of ripple the rings are closer together. The further away from the ripple the rings spread out and there is more time inbetween each ripple. Same wit an electric field. The more lines closer together means the stronger the field. The furth the lines are form each other mean a less strong field.