What is an example of an immutable type?

Could you please provide me with an example of an immutable type? I'm trying to understand how it differs from mutable types in the realm of programming. Could you explain how an immutable type behaves and why it's significant in ensuring data integrity and security? I'm particularly interested in the context of cryptocurrencies and blockchain technology, where immutability seems to play a crucial role. Could you elaborate on how immutable types contribute to the security and reliability of these systems?