"The" definition? If you wanted an authoritative definition, surely a dictionary would be the place to look?
My dictionary app says (abbreviated a bit):
1) the ability to become aware of something through the senses;
2) the state of being aware in such a way;
3) a way of regarding, understanding or interpreting something;
4) intuitive insight.
So, "perception" is both understanding something, either via the senses alone, or with the aid of other abilities such as logic or intuition, and the ability to do so. Meaning #3 carries the implication that perception is subjective and fallible, often partial.