In other countries they'd just be called recruiting agencies (they can do either permanent or contract jobs).
He's referring to contracting, where you work for one client at a time, almost identical to like an employee would but for the duration limit (and likely a company in between you and them to solidly the facade).
In contrast to what most people would call freelance, where you work for multiple clients at the same time, i.e. a dev agency of one.
Yeah, sorry. I got contractor and freelancer mixed up. It doesn't help that in Sweden freelancer/contractor/consultant are used interchangably for someone who invoices for their time instead of getting a salary.
The contracting agencies don't do any permanent position, they only do medium-to-long term contracts (3-24 months). The biggest is Northern Europe is probably https://www.verama.com/ (ex E-Work)
I did that a number of years ago ~2009 in Australia. If I recall the markup was ~8-10%. It was pretty much a big recruitment company (Hays) that also helped clients find short term contracts.