These are thin, clear plastic A4 sticky labels with a peel-off paper backing. You print on them using your inkjet printer, peel off the backing and stick them to anything! Customise your mobile phone, your laptop - anything with a hard, smooth surface! If you are reasonably careful applying them, the clear plastic is almost invisible. Of course you can print multiple designs on one sheet and then cut them out with scissors to make many stickers of any size out of just one sheet. I have also used a paper guillotine to cut a sheet into two A5 sheets, which printed fine.
Just one word of caution - the plastic is very thin (though strong) and rather subject to static electricity, so once you have peeled the backing off, the label tends to wrap around itself and stick to itself, which is very difficult to undo. So remove the backing gradually, sticking the label down as you go.