Hi friend!
The answer is in the name -- "Pseudo" meaning "not genuine but having the appearance of".
With the first terminals, there was always a piece of hardware attached with the associated device, be it display hardware or a serial port.
With windows, telnet and ssh, there came a need for software "Pseudo devices" to do the job of standing in for display hardware. They are "Pseudo Terminals" ... software that emulates Terminal hardware, handling input and output in the same way a physical device would so that the software connected is not aware there's not a real device attached.
Because now we have many applications which need to access the same piece of hardware, every app is using the hardware via a "pseudo" terminal.
Hope to help you!