Here’s a definition from the The National Center for Homeopathy:
Homeopathy is a system of medicine that is based on the Law of Similars. The truth of this law has been verified experimentally and clinically for the last 200 years.Let’s look at an example: If your child accidentally ingests certain poisons, you may be advised to administer Syrup of Ipecac to induce vomiting. Ipecac is derived from the root of a South American plant called Ipecacuanha. The name, in the native language, means “the plant by the road which makes you throw up.” Eating the plant causes vomiting.
When a group of healthy volunteers took this substance to determine the effects of this drug, they found that the drug induced other symptoms as well. The mouth retained much saliva. The tongue was very clean. There was a cough so severe that it led to gagging and vomiting. There was incessant nausea. While it is expected that vomiting would usually relieve the nausea, this was not the case.
Such an experiment, using healthy volunteers, is called a proving, and it is the homeopath’s source of information about the action of a drug.
Of what use could this plant be? If a person were suffering from a gagging cough after a cold, or a woman were experiencing morning sickness with incessant nausea that is not relieved by vomiting, then Ipecacuanha, administered in a minute dose, especially prepared by a homeopathic pharmacy in accordance with FDA approved guidelines, can allay the “similar” suffering.
Samuel Hahnemann described this principle by using a Latin phrase: Similia Similibus Curentur, which translates: “Let likes cure likes.” It is a principle that has been known for centuries. Hahnemann developed the principle into a system of medicine called homeopathy, and it has been used successfully for the last 200 years.