Interception
Man in the middle
A machine placed on the path between two parties, able to read and alter what is not protected end to end.
It can come from a hostile gateway, a forged DHCP or ARP answer, or a compromised network device. Plain HTTP and DNS are fully exposed to it; TLS keeps content private and detects impostors, as long as its warnings are respected. Switch protections and VPNs reduce the exposure.