Many line printers back in the day did 132 columns. As a result the popular DEC VT-100 had a 132 column mode to allow proper viewing of the output of programs without having to waste paper. It wasn't that great and was sort of hard to read.

As part of VT-100 compatibility, many subsequent terminals also supported 132 column mode.

Others have mentioned printers and older terminals that supported 80 and 132 column modes. That bled into other things. Like, for example, Gnome's terminal app has a couple of 132 column settings as selectable presets. Also, the framebuffer/vga console in Linux (and probably other OSes) can be set into a 132 column mode. It's an official "VESA mode" also.

Back in the day some terminals had a choice of 80 or 132 column modes. Since obviously the window (screen) didn't change size, this was achieved with a narrower font.

Monospaced, right?

yes, but using fewer horizontal pixels.

You used to be able to run old terminals in either 80 or 132 column modes.

GNOME Terminal's four presets are: 80x24, 80x43, 132x24, 132x43

I always kind of figured "132" was some arbitrary programmer decision, never knew it dated to old terminals. At least I recognize 24 and 43 as the number of lines old text modes (on, eg, VGA) had.

Some old SVGA cards from the 1990s had a ~132x60 mode (as well as a bunch of others), that could be activated in DOS with the RHIDE editor that came with DJGPP (no doubt there were other ways), or with SVGATextMode in Linux.

This.

I know the DEC VT340 was capable of 132 columns, as was an Apple II with a Videx Ultraterm card and a suitable (hi-res) monitor.

There are probably even more examples, but those two are what came to mind first.

Ahhh, the good ol’ DEC VT-240 CRT.