What are enums and why are they useful?

Question

Today I was browsing through some questions on this site and I found a mention of an enum being used in singleton pattern about purported thread safety benefits

Answer 1

Enums are like classes. Like class, it also has methods and attributes.

Differences with class are: 1. enum constants are public, static , final. 2. an enum can't be used to create an object and it can't extend other classes. But it can implement interfaces.