MEV stands for Maximal Extractable Value. It is the extraction of inherent value in the blockchain. In practice, MEV takes a few forms, the most popular ones are Sandwiches, Arbitrations and Backruns. Depending on the form, MEV extraction can have a positive or negative impact on the user's transaction. Merkle protects users from the negative MEV (Sandwiches) and captures the positive ones (Backruns).