Another way of saying the word kafir.

Those who say they belong to Ahmadiyya are proclaiming themselves "proud infidels", "rejectors", "deniers", "disbelievers", "an unbeliever", "nonbeliever" in Islam and the final Prophet Muhammad (may Allah's peace and blessings be bestowed on him).

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Ahmadiyya is the name of a sect that claims to be a part of Islam.
The belief of Ahmadis is very similar to the general Muslim belief. They believe in a prophet after Muhammad PBUH and their creed of school of thought is slightly different. Ahmadiyya is also a movement outside Islam that was created and founded heavily by the British Empire in India and mainly by the alleged prophet Mirza Ghulam Ahmad of Qadian; hence the term used to refer to them by many, "Qadiani".

Qadianism and Ahamadiyya are synonyms and refer to the same group of people.

However, they are rejected by the majority of the Muslim population over the world, there was even a council to declare them as apostates.