"Autosomal" means the gene involved is located on one of the numbered chromosomes. "Recessive" means that a child must inherit two copies of the pathogenic variant, one from each biological parent, to be affected by the disease. A carrier is a person who only has one copy of the pathogenic variant. A carrier usually doesn't show any symptoms of the disease.
If both biological parents are carriers, there is a 25% their child inherits both copies of the pathogenic variant and is affected by the disease. Additionally, there is a 50% chance their child inherits only one copy of the pathogenic variant and is a carrier.Learn more about inheritance patterns from the National Library of Medicine (NLM).