The name is what you call the event in a conversation ('are you going to Horizon too?'). It is short, usually one to three words.
The slogan is the line beneath the name that explains what happens or what you want people to feel ('Everything we are starts here').
Name and slogan work together: the name is the label, the slogan is the promise. A good event has both. People remember the name first; the slogan only works later, when someone looks more closely. Always start with the name; the slogan comes after.