What does 12.5 mean on the shutter speed?

It depends on where you are seeing this number.

Most shutter speed conventions do not use o1/12.5 of a second as a shutter speed; the closest would probably be 15 meaning 1/15th of a second, which is a very long/slow shutter speed usually producing blurs if you're not using a tripod. I can't think of a camera with that as a preset shutter speed but your camera might.

You may possibly be looking at an intermediate f-stop (between 11 and 16) being reported on your screen or wherever these are shown (your LCD?) when you are in shutter priority mode where you are setting a fixed shutter speed and then the camera automatically adjusts for f stop (aperture) based on WB and ISO and is sophisticated enough to report an f-stop between 11 and 16).