Simplify the following text for a Grade 6 native English-speaking person.
Original: J. Sainsbury plc is the parent company of Sainsbury 's Supermarkets Ltd , commonly known as Sainsbury 's ( also Sainsbury and JS ) , the third largest chain of supermarkets in the United Kingdom with a share of the UK supermarket sector of 16.5 % .
Simplified: Sainsbury 's is a supermarket chain based in the United Kingdom .