(uncountable) Mental, sometimes emotional process of comprehension, assimilation of knowledge, which is subjective by its nature.
(countable) Reason or intelligence, ability to grasp the full meaning of knowledge, ability to infer.
(countable) Opinion, judgement or outlook.
According to my understanding, the situation is quite perilous. I wonder if you see it this way, too.
(countable) An informal contract, mutual agreement.
I thought we had an Understanding - you do the dishes, and I throw the trash.
(countable) A reconciliation of differences.
The parties of the negotiation have managed to come to an understanding.
He showed much Understanding when he found out of my troublesome familial history.
All that people individually sense and feel of ourselves.