THIS IS THE SPACE AROUND YOU THAT YOU DON'T WANT OTHERS IN.
Sometimes, you get too close to your friends and they begin to back away or cower. This usually means you are too close. Instead of continuing to move closer to your friend you want to back away.
I know conversations can be exciting or you missed someone and you want to hug them, but that invades their personal space. Instead of hugging your friends, it is better to give a high five. Look how happy they are!