What is “Port” in Networking

Ports can be readily explained with an analogy:

Think of IP addresses as the street address of a block of flats (apartment complex), and the port number as the number of a particular flat (apartment) within that building.

If a letter (a data packet) is sent to the flats (IP) without a flat number (port number) on it then nobody knows who it is for (which service it is for). In order for the delivery to work, the sender needs to include a flat number (apartment number) along with the address to ensure the letter gets to the right domicile.