What is an 'invitation'?
The invitation? It's the announcement that you're having a party. The invitation should have the standard information: the date, time, and location. The invitation should also let the guests know what to wear. I even like to let people know whether it's a cocktail party or whether it's a barbecue, and how they should dress (as I mentioned a second ago). Because if it's a barbecue you want them to be casual. If it's a wedding, maybe you want them semi-formal, and maybe you want them formal. But the invitation should have some high-energy words to get people excited to come to your party.