The fear of public spaces or crowds.

This fear/phobia is pretty easy to explain.
If you have it, you're scared of crowds.
Many humans on one specific place makes you very Uncomfortable or even makes you get a panicattack.
These humans are scared of being in situations were escaping might be difficult.
Like for example travelling with public transport.
Because there mostly are crowds of humans and there isn't an escape.

Look at theses pictures.
Think yourself in that situation.
Would you feel uncomfortable or would you even be scared?
If yes you might have Agoraphobia.