An impression is a recorded display event: a system logs that content, such as an ad, banner, or message, was served or rendered. It does not prove that a person noticed it, read it, or trusted it. In security and fraud analysis, that distinction matters because raw impression counts can look impressive while representing little real attention.
Attackers and defenders both care about impressions. Ad-fraud systems may try to inflate them with bots, hidden frames, or repeated loads, while malicious campaigns can use large impression volumes to spread phishing lures or malvertising. Security teams reduce this risk by checking viewability, dwell time, unique-user signals, and downstream actions such as clicks or form submissions. In short, an impression is useful telemetry, but by itself it is only evidence of delivery, not engagement.