Nonsense. Ther are many definitions that could be considered "main".
The main anthropological definition goes something like - a society for the purpose of studying and enacting magical, ritualistic, or other religious activities.
Or, "a relatively small group of people having religious beliefs or practices regarded by others as strange or sinister." - from the definition supplied by Google.
Merriam-Webster says:
"Full Definition of CULT
1
: formal religious veneration : worship
2
: a system of religious beliefs and ritual; also : its body of adherents
3
: a religion regarded as unorthodox or spurious; also : its body of adherents
4
: a system for the cure of disease based on dogma set forth by its promulgator <health cults>
5
a : great devotion to a person, idea, object, movement, or work (as a film or book); especially : such devotion regarded as a literary or intellectual fad
b : the object of such devotion
c : a usually small group of people characterized by such devotion"
ANY religious organisation qualifies under at least one of those definitions.