Simple Definition:

Haemophilia is a medical condition that affects the blood’s ability to clot [form a thick mass to stop bleeding] properly. People with haemophilia may experience prolonged bleeding after an injury or even spontaneous bleeding without any apparent cause. For example, a person with haemophilia may bleed for a longer time after getting a small cut or bruise, and they may also have frequent nosebleeds or bleeding gums.

Very Simple Definition:

Haemophilia is a condition where a person’s blood doesn’t stop bleeding easily, because the blood at the injury takes longer to become dry and hard. People with haemophilia bleed for a longer time after getting a cut or bruise. For example, if someone with haemophilia gets a small cut, it may take them longer to stop bleeding compared to someone without the condition.