Impressions
The number of times you appeared in front of someone. It rises even when you appear for searches that will never buy.
Why it matters when you read an offer
The easiest number to show in a report and the one least connected to revenue. It grows even when you appear in front of people who will never buy anything from you.
What it looks like in an offer
A report leading with impressions: two million views. The big number does not mean visitors, let alone customers.