#extend("trunk"): #export("body"):
An alt account lets you post as someone else, while still being yourself. If, for example, you run a certain type of Shadow Event, you might make an alt account named after the event you run. You can then post about your event in a way that makes it clear you're the one running it, and still switch back to your main account when chatting with your friends.
Remember that all your accounts are subject to the Code of Conduct, and are all jointly subject to the rulings of the moderators.