Man-in-the-middle attack definition:

Answer: See the explanation

Explanation:
BD
Man-in-the-middle attacks: Someone or something is between the two devices who believe they are
communicating directly with each other. The “man in the middle” may be eavesdropping or actively changing
the data that is being sent between the two parties. You can prevent this by implementing Layer 2 dynamic
ARP inspection (DAI) and Spanning Tree Protocol (STP) guards to protect spanning tree. You can implement it
at Layer 3 by using routing protocol authentication. Authentication of peers in a VPN is also a method of
preventing this type of attack.
Source: Cisco Official Certification Guide, Threats Common to Both IPv4 and IPv6, p.333