MRSA is a type of bacteria that's resistant to several widely used antibiotics. This means infections with MRSA can be harder to treat than other bacterial infections.
The full name of MRSA is meticillin-resistant Staphylococcus aureus. You might have heard it called a "superbug".
MRSA infections mainly affect people who are staying in hospital. They can be serious, but can usually be treated with antibiotics that work against MRSA.