what is enum in mongoose code example

Example 1: enum in mongoose

var userSchema = new mongooseSchema({
   userType: {
        type: String,
        enum : ['user','admin'],
        default: 'user'
    },
})

Example 2: mongoose model enum

enum Role {
  ADMIN = 'ADMIN',
  USER = 'USER'
}

{
    type: String,
    enum: Role,
    default: Role.USER,
}