The definitions of MQL and SQL (SAL) should be spelled out, and agreed upon, in a service level agreement (SLA). The SLA outlines the terms of how sales and marketing will work together. The SLA should define what MQL and SQL look like, as well as state the time frame and process each team must follow. For example, an MQL has reached a score of 75 through a combination of content engagement and web engagement and fits the ideal customer profile. It must be accepted by sales or sent back to marketing within 24 hours of being assigned. The SLA should be drafted together by both marketing and sales leadership and signed off on by both parties.
Of course, regardless of how they enter into your funnel, your goal as a marketer is to move them through the multiple stages that will take them from prospect to buyer. And once they're aware of you, you need to build their interest. To do this, you need to establish a relationship with the customer. You might have enticed them with a great offer (lead magnet) to grab their email address, but actually moving them through the funnel is a far greater challenge.
If you're wondering what a sales funnel is, simply imagine a real-world funnel. At the top of that funnel, some substance is poured in, which filters down towards one finite destination. In sales, something similar occurs. At the top, lots of visitors arrive who may enter your funnel. However, unlike the real-world funnel, not all who enter the sales funnel will reemerge out from the other end.