Most SEA platforms primarily work on a Cost-Per-Click or Pay-Per-Click base. Therefore, in most cases, the advertiser is focused on getting that relevant click. However, an ad impression should not be disregarded too easily.
What is an Impression? An impression, also called View, is counted each time your ad is shown on a search results page or other site which is part of the advertising network, like Gmail for Google.
Unlike Clicks, Ad Impressions are free of charge when the CPC bidding is used. If CPM Bidding is used an impression is not free. Unless your ads have Click-Through-Rates of 100%, you will always have more Impressions than Clicks.
Impressions in AdWords
In some cases, only a section of an ad may be shown. For example, in Google Maps, Google may show only your business name and location or only your business name and the first line of your ad text.
When someone searches using Google Search Network, an impression can be counted when one of these events occur:
-A person begins to type and then clicks anywhere on the page like a search result, ad, or related search
-A person types a search and then clicks the "Search" button, presses Enter, or selects a predicted query from the drop-down menu