a “terminal multiplexer” is a software application …

• https://en.wikipedia.org/wiki/Terminal_multiplexer

Features:

• persistence
• multiple windows AKA screen splitting, screen tiling (my most wanted feature) – other applications have that as well (and for the same purpose): emacs, KDE konsole, …
• session sharing
• …

Implementations:

• https://en.wikipedia.org/wiki/Terminal_multiplexer#Implementations
• https://en.wikipedia.org/wiki/GNU_Screen
• https://en.wikipedia.org/wiki/Tmux
• https://github.com/ruda/splitvt / https://slouken.libsdl.org/projects/splitvt/
• …