Network switch separate Ethernet port?

In most cases, a switch is used to expand a LAN (network). To do so, one port has to go "up" to the rest of the network, like another switch or a router. That is usually called an "uplink". Then, the other 4 ports are for local machines, etc.

In some switches, the "uplink" can be used as a regular port as well (if no connection to anything else is needed). Also, on some switches, only the uplink port has auto polarity detection (MDI/MDIX), so one can use any cable - straight or crossover. Newer switches have auto MDI/X on all ports.

Thus, in normal use, a switch always has an uplink, and vendors tend to identify that as a separate "port", though in real life it is somewhat meaningless. Modern switches don't really care any more how you wire them.

The picture you show is a standard 5 port switch, and the only thing about it is that is uses a "4 Ethernet port" connector, then a single connector. That is because they usually do not make 5 port Ethernet connectors (physical connector strips), they have to use a 4 and a one. Connectors are usually made in strips of 4 or 8 (sometimes 12 or 16), and higher end switches are all 8 port, 16, 24 ports, etc. It is only these cheaper 5 port switches that need to break apart the connector strips (use a 4 plus a single) to make a 5 port physically....

It used to be that the 4 ports would be for connecting devices, while the separate 5th port would be the Uplink port that you'd use to connect to other switches. But now with auto-sensing switch ports and more intelligence, there's not usually any difference between the ports anymore.

Now it's more because of cheaper parts. They often make ports in blocks of 4 because most switches are in multiples of 4 (8, 16, 24, 48 ports). So to make the 5 port switch they just use the existing 4 port and single port parts instead of designing and manufacturing a separate 5 port part that would only be good on this type of switch.