"Whats that?"
It's a multi-node system (two, three or more units) that all "work together as one".
It's time for YOU to "do the investigating" and find out which mesh system would work for you.
I've had good performance with the Linksys Velop.
There is also Netgear Orbi, eero, google wifi, Ubiquiti "Amplifi", and numerous others.