Horizons is a bar and restaurant that is cheaper, has longer hours and a different menu than 360 which is one floor above it in the CN Tower. The chef and sous chefs are the same for both restaurants.
A big difference is that 360 comes with a free elevator ride, whereas you had to pay general admission to get into Horizons. That said, you will most likely pay a little less overall for Horizons. Horizons Restaurant does not rotate like 360, but I kind of like that as well, as your view is panoramic and allows you to feel stationery.
360 absolutely requires a main dish to be purchased by every person at the table, whereas Horizons has no minimum purchase.