The two stages
A marketing-qualified lead (MQL) is someone who has shown enough interest, and fits the target profile well enough, for marketing to pass them to sales. Typical signals are downloading a guide, attending a webinar or visiting the pricing page several times. A sales-qualified lead (SQL) is one that a salesperson, often an SDR, has spoken to and confirmed has a real need, a reasonable fit and a reason to talk now. In short, an MQL shows interest; an SQL shows intent.
Example
A marketing manager downloads a pricing guide and attends a webinar, so she becomes an MQL. An SDR calls, learns her team is replacing its current tool next quarter and that she is leading the evaluation, and books a meeting. She is now an SQL.
Why the distinction matters
Marketing and sales often disagree about lead quality. Clear MQL and SQL definitions give both teams the same rules: what earns a handoff, who follows up and how fast, and what has to be confirmed before a lead counts as sales pipeline. Without them, reps waste time on people who were only curious, and good leads go cold while nobody owns them. Tracking how many MQLs become SQLs also shows whether marketing is attracting the right people.
What it means for reps
Calling an MQL is a warm call, not a done deal. The person may barely remember the download. Practice an opener that references what they did without overstating it, then qualify with a few direct questions about need, timing and who is involved. In interviews, explaining MQL vs SQL clearly, and describing how you would qualify one, shows you understand how the funnel works.