Wasted impressions term can have two different meanings according to the perspective.
From the advertiser’s point of view, a wasted impression is an ad impression which is not viewed due to bad placement (below the fold for instance) or an ad impression delivered to bad eyeballs (outside the campaign target).
From the publisher POV, it is an ad impression which is not sold.
In the example below, if there is not bid for an ad impression (or bids below the floor price), it becomes a wasted impression.
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