What is equilibrium in scientific terms? I need it broken down as simple as possible please because I don't understand it.

In science, literature, and everything, equilibrium has the same meaning. The meaning simply put, is balance. If you wanted a sentence example, it could be something like:

'He sat down to try and recover his equilibrium.'

Or

'They can't maintain enough equilibrium to ride a bike.'

I hope you understand the meaning now?

particle   p is an electron and particle q is a neutron