Impressions stem from experience. They are mental presentations or constructs.
Impression is polysemous. That simply means it has multiple definitions. In science and philosophy it does a lot of heavy lifting. It can mean a sensory experience, a mental presentation, an initial judgment, or the lasting effect of an experience.
To clarify, here’s another one of my word paintings. In TST, impression is used as an umbrella term bridging sensory, perceptions, and ideas. There are three regular uses of the term in TST: live, original, and current. Live impressions exist in the now. Some are immediately forgotten; a few are retained for a lifetime. An original impression refers theoretically to the first version of an impression, as it was initially formed. A current impression is how that impression is represented by the mind now, potentially after being recalled and reinterpreted.
Stoics focus on examining impressions before granting assent to them. In my discussion of Al-Farabi’s potential intellect, I compare the developing mind to a blank canvas that accumulates impressions like a painting continuously being painted. Hume distinguished vivid impressions from the generally fainter ideas that arise from them, including those recalled through memory.
Modern cognitive science explores how experiences are processed, retained, recalled, and sometimes altered. To be clear, organizing impressions into live, original, and current is a TST distinction, not an established scientific classification.