Most likely a step down transformer. Is there any text in those labels, as there you will find the info, but the picture has this all washed out.
Looks to be around 100VA, so you can use the old trick of using a 40W incandescent lamp in series with the mains, or another 12VAC transformer ( not electronic, good old iron and copper) and apply to the one terminal with a series 21W car light bulb in series, and measure the actual voltages on the terminals and then you can work out both the ratios and which is the primary as well to use it.