Amazon PPC glossary
Impression share
Impression share shows how much of the available audience you actually reached. A low share on a keyword that works well can mean your bid or budget is holding you back.
Example
A keyword you target could have shown your ad 1,000 times. It showed 400 times. Your impression share is 40%.
Where it matters most: Book 5, The Advanced PPC Clarity Guide, in the chapter “Scaling or Protecting a Winning Campaign.”
Go deeper
The glossary gives you the one-line answer. The Advanced PPC Clarity Guide explains why it matters and what to do about it.