I hear the terms mutant and variant used a lot in the media about the COVID virus. What does it mean?

For viruses, the term mutant means that the RNA sequence (genetic message for the virus) has undergone a change (mutation). The resulting virus with the mutation is called a variant, eg. you will hear about Kent variant, South African variant, Brazilian variant. Each of these variants have different mutations. Mutations occur in every living organism including humans, viruses and bacteria (antibiotic resistance is caused by mutations).