What is a Mev sandwich?

Could you please clarify for me what exactly is meant by the term "Mev sandwich" in the world of cryptocurrency? Is it a specific type of transaction or strategy that involves manipulating market conditions to gain an advantage? How does it differ from other forms of market manipulation, and what potential risks or consequences could it have for investors and the overall health of the cryptocurrency market? I'm interested in understanding the intricacies of this concept in more detail.