Sole Trader is another term for self employment. Sole Traders are businesses owned by just one person and may not take on partners or shareholders but can have employees.
Sole Trader businesses are a more common type of business than Limited Companies. They are usually small but are still able to make large profits!
Self employment is a good option if you want to test your business idea as it’s fairly simple to switch over to a Limited Company structure (where the business is its own entity rather than the business being you).