For context, I assume you've encountered some such phrase as "cult worship" or the "cult" of a particular deity in a text. If so, you should know that this particular usage of "cult" is different from the common usage of the word, referring to e.g. the Jonestown cult.

In classical scholarship, by contrast, "cult" just means worship, in the sense of the religious observances and rituals that belong to devotion to a deity. This is because one of the Latin words for worship is cultus, from the vebr colo, "to cultivate"; it is often used both of humans' observances towards the gods and of the gods' special protection and care of a place.

If, on the other hand, you've heard of modern worshippers of the Greco-Roman gods (who do exist) being referred to as in a "cult," that usage is more in the modern sense, simply because tiny religions often perceived as eccentric are often referred to as cults. But I would guess that we were talking about the former usage.