If the network in question is a LAN or WAN, every node must have a MAC address if it is at least a data link layer device, as defined in the OSI model. In the Internet, many network nodes are host computers, identified by an IP address, and all hosts are nodes. However, datalink layer devices such as switches, bridges and WLAN access points do often have an IP host address (except sometimes for administrative purposes), but are considered as network nodes.
In telecommunications, a node is a specific location in a telecommunication network. In cable television systems (CATV), this term has assumed a broader context and is generally associated with a fiber optic node. This can be defined as those homes or businesses within a specific geographic area that are served from a common fiber optic receiver. A fiber optic node is generally described in terms of the number of "homes passed" that are served by that specific fiber node.
A node can also be described as a device having local processing capability(has integer processing capability). EX: PC without network card, Mobile Phone
If we put some network interfaces or network interface card, a node can be connected to a network.