Simple Definition:

Comprehension is the act of understanding or grasping the meaning or significance of something. It involves interpreting and making sense of information, ideas, or concepts [interpreting]. For example, when reading a book, comprehension is the ability to understand what the text is saying and being able to answer questions about it.

Very Simple Definition:

Comprehension is understanding something. For example, when you read a book, comprehension is knowing what the book is about and being able to answer questions about it.