What is an instance?

Some don’t like this comparison, but effectively think of lemmy in similar forms to e-mail, IE you can e-mail your friend who uses a different mail service, by adding @whatever.com to their username. the whatever.com in e-mail that’s called a domain usually, but in lemmy that’s considered the “instance”. The only difference is rather than just saying “that’s not an address” lemmy assumes if you don’t specify, you must mean the one where you are.