Okay kiddo, have you ever been to a restaurant where they sell sandwiches, cheeses, and meats that you can buy and take home with you? It's called a delicatessen, or for short, "deli".
They have a lot of different kinds of food, but they're all special because they're made in a certain way that makes them taste really good. The meat, for example, might be "cured" which means that it was treated with spices and salt that make it last longer and taste better.
Some people really like going to a deli because they can pick out exactly what they want and how much of it they want. They might like a lot of variety, or maybe they just really love one kind of sandwich that they can't get anywhere else.
So a delicatessen is like a special type of restaurant that sells fancy sandwiches and other foods that are made in a special way to taste really good.