My definition of a religion is that it's a belief system.
The reason why religions exist is because we humans need to have beliefs. Bad weather, deaths,... were explained by the anger of God thousands of years ago. In our times, we use religion (beliefs) to explain the superiority of the human being.
We are indeed slowly moving towards religions where instead of placing a superior entity at the top of our belief system, we put ourselves at the top. The increasingly popular humanism is the perfect example of that.
While humanism isn't seen as a religion in our society, it definitely is according to my definition of a religion. Humanism places the lives of humans at the center of everything. Though, this is entirely based on beliefs as the truth is that no entity is superior to another one, in my opinion. While we are "smarter" (whatever your definition of being smart is) than all the other animals we know of, this doesn't make us superior.
If attributes like intelligence determined who dominates who in nature, we would probably be dominated by elephants because of their size and cheetahs because of their speed. Though, they are clearly not dominating us, so why would our intelligence be a valid reason to dominate them?
Veganism is also a religion according to my definition. Liberalism and communism also fall under the religion umbrella. They all are, as each of them relies on a set of beliefs.
Even if the idea that religions are quickly losing popularity in our "modern" society is widely accepted, I strongly disagree with that. Religions are definitely not over in my opinion and probably never will as believing in something is much easier than accepting the void, the emptiness of the universe and the lack of reasons to live as a human being.