My iMac shows another connect computer what is it?
It is an Epson device connected to your WiFi network, most likely a printer. However, it could also be a scanner, projector or even a pair of smart glasses.

If it's only new to your network, it could be that someone has plugged a USB stick (or similar) into a printer etc.

I wouldn't be worried unless you don't actually own an Epson product.