Haemophilia is an inherited condition that affects the blood's ability to clot.
Normally, when you cut yourself, substances in the blood known as clotting factors combine with blood cells called platelets to make the blood sticky. This makes the bleeding stop eventually.
However, in haemophilia, there aren't as many clotting factors as there should be in the blood. This means that someone with the condition bleeds for longer than usual.
The condition is passed to a child by one or both of their parents.