1. A feeling or an idea which is formed without thinking about it very much: After writing his first short story, James asked his friend to read it and give his first impressions and comments about it.

Ted’s parents had a very good impression about his new girlfriend who seemed to be very friendly and courteous to them.

2. A visible representation of an item or of somebody, as in a picture: The police asked the robbery victim to give his impression of the culprit so they could try to find and arrest him or her.
3. A marking which is imprinted on the outside of something: Jane thought that the impressions of the cartoons on the coffee cups at the restaurant were very amusing.
4. The formation that is made of the teeth by having them pressed into a soft material: While Nils was at his dentist, there was an impression made of his dentures in preparation for the new tooth which was missing.
5. An effect or influence that something or someone has on another person's thoughts or feelings: First impressions are important, however they can be misleading and inadequate for knowing what is really true.

The saleswoman's pleasantness and cheerfulness always left positive and lasting impressions on her customers.