A click is when a person clicks on your paid Text Ad on Google’s Search Engine Results Page.
A click is counted in Google Ads anytime someone clicks on your Text Ad.
Highly targeted Text Ads that are relevant to the people seeing them have a higher chance of being clicked.
How often your Text Ad is clicked can give you an indication of whether or not your Text Ad is inviting to the people searching for your products or services, although this is not the sole deciding factor.
Source: Definition: Click