An MQL (Marketing Qualified Lead) is a lead that meets defined criteria. Marketing checks it before passing it to sales: can this person really become your customer? If the answer is "yes" it's an MQL; if "no," it stays a plain lead.
Why does the MQL matter? Because the sales team's time is limited and worth more than the lead itself. Every empty call is time stolen from a real deal. The MQL protects exactly that time.
When a lead becomes an MQL
Criteria differ per project, but usually rest on four questions: (1) is the problem present now; (2) is there budget; (3) is this person a decision-maker; (4) do they fit your ICP. A lead that answers "yes" to all four is an MQL.
Measure MQL quality, not quantity. Working with 10,000+ MQLs teaches one simple rule: lead count means nothing on its own — the quality that converts to sales is what decides.