What are immutable types?

Excuse me, could you please elaborate on what immutable types are? I've been hearing a lot about them in the context of programming and data structures, but I'm still a bit hazy on the concept. Are they related to cryptocurrencies or finance in any way? If so, how does their immutability contribute to the security or efficiency of transactions in these fields? I'm particularly interested in understanding how they might affect blockchain technology and the way cryptocurrencies are handled. Could you provide an example or two to illustrate the concept further? Thank you in advance for your clarification.