What does congruence mean?

We read a book called Big Bushy Mustache.  It is about a little boy who looked a lot like his mother but he wanted to look like his dad so his dad   His dad helped him by making him a mustache.  We learned that mustaches need a line-of-symmetry and is congruent on both sides.  Miss Melanie's husband, Mr. Kevin, came to our classroom to help us make congruent mustaches.  We looked super cool with help from Mr. Mustache!  Also, one of our vocabulary words was 'disguise'.  The kids had a blast making disguises.