What is the difference between an MQL and an SQL?

An MQL is an opinion, not a commitment. Marketing decides this person is ready to hand over, based on who they are plus how they have engaged. It is the top of the handoff, not proof of a deal.

An SQL is the one that should drive forecasting. Sales has actually had a conversation and confirmed there is a real opportunity worth pursuing.

The step most companies skip sits between the two: the sales accepted lead, where sales explicitly accepts or rejects the MQL with a reason. Without it, nobody can tell whether marketing is passing junk or sales is ignoring good leads. Adding that accept or reject step is the cheapest way to settle arguments about lead quality.

One caution on measurement: comparing your MQL to SQL rate against an industry benchmark is close to meaningless, because every company defines an MQL differently. Track your own trend instead.