Off-payroll means getting paid for your work through other ways than through a salary (also called “payroll”). For example, if you’re a self-employed freelancer, you get paid through an invoice.
Simply being off-payroll does not mean that you’re not an employee. The new IR35 law states that if you’re an off-payroll worker and your client treats you like an employee, then your client must place you on the payroll and pay employment taxes for your work.
If you’re an off-payroll worker and want to know how HMRC sees the relationship between you and your client, you might want to check out the CEST tool from HMRC.