Simple Definition:

Surface tension refers to the tendency of the surface of a liquid to resist external force. It occurs because the molecules on the surface of a liquid are tightly packed together and form a “skin” that holds the liquid together.

For example, when you pour water into a cup, the water forms a dome on the top of the cup because the surface tension of the water is holding it together. Another example is when insects like water striders [an insect with very long legs] can walk on the surface of water due to the high surface tension of water.

Very Simple Definition:

Surface tension is what makes water droplets stick together or “bead up” on a surface. It’s like the surface of the water is covered in an invisible skin.

Example: When you pour water on a table, it forms droplets instead of spreading out evenly because of surface tension.