Understanding a concept means you get it. The meaning of understanding is a mental grasp : How to use understanding in a sentence.
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Understanding is a relation between the knower and an object of understanding. Comprehension usually used with of. Or about how something works:
Your understanding might be that your mother will always drive you to school if you miss the bus.
Knowledge about a subject, situation, etc. Understanding implies abilities and dispositions with respect to an object. Both comprehension and understanding can be used to talk about someone's ability to understand something. He noted bond's apparent lack of.
