broadcast domain The set of nodes that will all receive a broadcast message transmitted by any one of the other nodes. All of the computers on a LAN are in the same broadcast domain. Two networks connected by a router, however, are in different broadcast domains, because routers do not forward broadcasts. Basically the same as an IP network. Rule for (IP) network: all hosts in the LAN are in the same IP network and no hosts of this IP network are in other LANs.

internet(work) a group of connected networks, a network of networks. Connected by routers. IP binds them together. The Internet (capital I) is the worldwide internetwork that runs on IP. IP is the one protocol to rule them all.

collision In old/obsolete hub-based Ethernet and in WiFi, a condition in which two computers transmit data at the same time (in the half-duplex network), and their signals both occupy the same medium (cable or frequency), resulting in garbled signal.
CSMA/CD Carrier Sense Multiple Access with Collision Detection was the decentralized protocol an Ethernet NIC would use to gain access to the shared medium: waiting if any signal is detected, transmitting its frame when the medium becomes free but "listening" to detect any collision of its frame, and backoff a random amount of time before retrying to get the medium. Turned off in switched full-duplex Ethernet NICs.
CSMA/CA Carrier Sense Multiple Access with Collision Avoidance is used by WiFi nodes to reduce collisions. Receiver sends an acknowledgement frame to sender. If sender doesn't receive ACK, assumes its message never received, and sends again. Optionally, explicit RTS (request to send, by the client) and CLS (clear to send, by the WAP) frames to eliminate the hidden transmitter problem (a node within range of WAP but not of a transmitting node could listen to medium, sense it unused, transmit and collision occur at the WAP). WiFi is a half-duplex for the entire network: only one transmission is happening at a time in the whole WiFi network (all nodes share the same radio channel).

Obsolete terms:
collision domain all the nodes that share a half-duplex network, in which any two nodes transmitting at the same time results in a collision. Full-duplex switched Ethernet eliminates collision domain. Segment referred to the LAN or collision domain. Switch provides microsegmentation of a segment per port.