A sales funnel is the model of how a lot of leads become a few customers. At the top you have every lead the company touches; each stage — outreach, qualified meeting, demo, proposal, close — filters more out, until only the won deals fall out the bottom. The SDR and BDR own the top: their job is to make the top wide and the qualification honest so real meetings don't leak. The account executive owns the rest.
In plain English
Imagine water pouring into a funnel. A huge amount goes in at the top, and only a stream comes out the bottom. Sales works the same way: most leads won't buy, so you need many more at the top than you want at the bottom. The difference between a good funnel and a bad one is usually leaks — stages where too many real deals fall out. Where your team leaks tells you what to fix.
Why it matters to you
Funnels and pipelines are used almost interchangeably, but the emphasis differs: a funnel is the shape of the math (many in, few out), while a pipeline is the list of deals in front of you. As an SDR, your metric is how many qualified meetings you feed the top — widening the funnel is literally your job. When a manager says "the funnel is leaking," they mean leads that should have become meetings or demos went quiet. Knowing which stage leaks is how you decide where your effort goes.