--The concept of ruby --A box (object-oriented) that contains multiple data and processes (methods) together. Something like a blueprint.
--The concept of rails ~~ Ruby ~~ --It must be a class, but it always has a table (database) corresponding to the model. --For example, the Post model has a posts table (the table contains multiple data, so the name is in the plural) => On the contrary, the model name must be named in the singular.