An MQL is a lead the marketing team thinks is ready for sales. The qualifying criteria are usually a mix of fit (matches ICP) and behaviour (visited pricing, downloaded a high-intent asset, attended a demo webinar). Each company defines its own threshold, which is where most disagreements live.
For agencies, the MQL definition is the contract between marketing and sales. If sales rejects half of MQLs as junk, either the criteria are wrong or marketing is gaming the number. Either way, reporting becomes meaningless until the definition is renegotiated.
MQLs are leading indicators, not outcomes. Optimising the marketing budget against MQL volume without checking MQL-to-SQL conversion and SQL-to-close rates is how you end up with great-looking dashboards and a stalled pipeline.