Your impression of a person or thing is what you think they are like, usually after having seen or heard them. Your impression of a situation is what you think is going on.

If someone gives you a particular impression, they cause you to believe that something is the case, often when it is not.

An impression is an amusing imitation of someone's behaviour or way of talking, usually someone well-known.

An impression of an object is a mark or outline that it has left after being pressed hard onto a surface.

If someone or something makes an impression, they have a strong effect on people or a situation.

If you are under the impression that something is the case, you believe that it is the case, usually when it is not actually the case.