As a rule, a worker would be a person who undertakes work or services for an employer. Workers may be working under a contract of employment - but not always.
WORKER: Generally, you would have 'worker employment status' if:
You have a verbal or written contract (or an arrangement) to do work or services 'personally' for a reward.
Your 'reward' is money or a benefit in kind (e.g. promise of work or a contract).
You have limit rights to send another person to do the work (such as subcontracting).
You must turn up for work (whether you want to or not).
Your employer provides the only work you have while a contract or arrangement lasts.
You do not carry out the work as part of your own limited company where the 'employer' is a client or a customer.
Worker Employment Rights
There are core work rights and protections afforded to all 'workers'. Though very similar for employment status purposes, not all workers get classed as employees. As a rule, these groups would have worker status (but not employee status).
Most freelancers
Short term casual workers
The majority of agency workers
Under UK labour laws workers have entitlement to certain employment rights. Thus, a worker would get: