A query regarding cock milking

It’s been ages since I last posted here, and what better way than with a query. Please bear with me; this feels like one of those questions that should be common knowledge… I’ve spent the past few years in the BDSM community, and during that time I keep hearing about cock milking mentioned often enough. Yet it turns out I’m still not entirely clear on what it actually means. So here is my main query: specifically, what does ‘cock milking’ mean? Also, if you need a moment to think before answering, thanks in advance…