In the UK a contractor could be someone from an outsourcing company as you suggest or they could be an independent service provider working on their own. This is very common in software dev here when you require someone with specific skills.
If you’re the latter kind then you’d be wise to bill on deliverables rather than time.
If you don’t you could run into a well known tax reg called HMRC IR35. It bars independent contractors from acting like “disguised” employees. It’s a world of pain if that happens.
The US allows companies to fire long-term employees without cause and replace them with indentured servants.
We're the ones who actually hosted the cotton fields full of slaves, after all.