A recorded selection of a link or control, counted according to the relevant platform’s rules.
A click is a recorded interaction with a link or control under a platform’s measurement rules. In search reporting, it commonly refers to a user selecting a result that leads toward a website. In website analytics, a click event may instead describe a particular button or link on the page.
Those are different observations. A search click does not necessarily equal one analytics session, and a button click does not necessarily mean the intended action completed. Check the actual metric definition and implementation before comparing counts from different systems.
A click count is not a count of unique customers. A person may interact more than once, while reporting rules can aggregate or exclude particular interactions. It also does not establish that the destination loaded successfully or that the visitor found the information useful.
Takeaway: Name the measured interaction precisely in reports. Use search clicks, telephone-link clicks and completed form submissions as separate measures rather than calling all of them leads.
Example
A visitor clicks a quote button but leaves after the form opens. The button event can show interest in the next step, but it does not prove a quote request was submitted. A separate, tested completion event is needed for that claim.
What to check
Keep the platform, date range and event or report name beside the count. Test important controls and destinations. Investigate discrepancies without assuming that two differently defined click totals should match exactly.
For more detail, see Search Console impressions, position and clicks.