What is immutability in Ethereum?

Could you kindly elaborate on the concept of immutability in the context of Ethereum? I'm curious to understand how this principle plays a pivotal role in the blockchain technology. How does immutability ensure the security and reliability of transactions within the Ethereum network? Also, could you explain the technological mechanisms behind it? I'm interested in knowing how it differs from other blockchain platforms and what makes it unique in Ethereum's case. Thank you for taking the time to answer my questions.