"X-linked" means the gene involved is located on the X chromosome, one of the sex chromosomes. Biological females have two X chromosomes (XX) while biological males have an X and a Y (XY). "Recessive" means that a female child must inherit two copies of the pathogenic variant to be affected by the disease. Because males only have one X chromosome, only one copy of the pathogenic variant is enough to cause the disease. Biological females who have only one copy of the pathogenic variant are called carriers. A carrier usually doesn't show any symptoms of the disease.
If a female parent is a carrier of an X-linked recessive pathogenic variant, there is a 50% chance their male child inherits the pathogenic variant and is affected by the disease. Additionally, there is a 50% chance their female child inherits the pathogenic variant and is a carrier. If a male parent is affected by an X-linked recessive pathogenic variant, there is a 100% chance their female child inherits the pathogenic variant and is a carrier. However, there is a 0% chance their male child inherits the pathogenic variant.
Learn more about inheritance patterns from the National Library of Medicine (NLM).