A voluntary agreement, given willingly, to a specific sexual act, at a specific time. The person giving consent fully understands what is happening, is old enough to consent, and is mentally capable of giving consent.
The law requires that a person take reasonable steps to find out whether the other person is consenting. The age of consent to sexual activity in Canada is 16. In some situations, a person must be 18 years old to consent to sexual activity (if the other person has a relationship of trust or authority over them, if it involves exploitative activity, if they are dependent on the other person, etc.).