"Looking glass" is an antiquated term for a mirror or reflective surface, dating back to Lewis Carroll's "Through the Looking Glass" novel. However, there are plenty of synonyms for this term that are much less archaic. For instance, we might say "mirror," "reflective surface," "speculum," "looking glass," "pane," "glass," or "plate." Each of these is a perfectly acceptable term for the thing we use to observe our own reflections. While "looking glass" may have a nice ring to it, it's certainly not necessary to use it in everyday conversation. Nevertheless, it remains a charmingly old-fashioned term that has become synonymous with certain whimsical stories and literary traditions.