Simple Definition:

Homeopathy is a form of alternative medicine [a type of healthcare that is different from what is taught in medical schools], which aims to treat illnesses by using highly diluted substances [mixtures that have been made weaker by adding more liquid] that would cause similar symptoms in a healthy person. It is based on the idea that “like cures like,” meaning that a substance that can cause symptoms in a healthy person can be used to treat similar symptoms in a sick person.

Examples:

• A homeopathic remedy for a headache might be made from a highly diluted form of a substance that would normally cause headaches, like belladonna [a poisonous plant].
• Homeopathy might use a highly diluted form of onion to treat someone with watery eyes and a runny nose due to allergies.

Very Simple Definition:

Homeopathy is a different way to treat illness. Homeopathy uses a tiny amount of a substance that normally creates an unwanted condition, in order to cure the same condition. For example, if you have a headache, a homeopathic doctor might give you a bit of water that has a tiny bit of a plant that can give headaches.