I regularly SSH to my computers and servers and, on some of them, I was getting the following warning message:

'ansi+tabs': unknown terminal type.

This was just a warning and everything worked perfectly. But, still, having a warning message was not very, ahem, professional…

I have just found the cure: you need to have additional terminal definitions installed on the remote computer. On Red Hat / CentOS / Fedora, do:

dnf install ncurses-term

and on Debian, CentOS and derivatives:

apt-get install ncurses-term

and everything will be fine.