What does dharma actually mean? Everyone uses it differently.

You're right that everyone uses it differently, and they're not wrong to. The word comes from the Sanskrit root dhṛ, to hold or support. At its simplest, dharma is what holds things together.

From there it grows several meanings: the order of the universe, right conduct and social duty, and svadharma, the path that belongs to you. Buddhist and Jain traditions use the same word in their own ways too.

So when someone says dharma, it's worth asking which of these they mean. Often it's more than one at once.