what does memtest86+ serial console mean

Two options.

  • memtest86+; used for boxes that have a screen attached

  • memtest86+ serial console 115200; used for headless boxes that have a serial terminal/console attached; the 115,200 is the speed (115,200 bps) or the fastest old serial connections (think RS232; well before USB) could reliably achieve before needing to modulate-demodulate signal etc