Ombre hair has been pretty popular for awhile now. It can also be called dip dyed hair, but that often refers to some kind of crazy color, like when I died my ends pink two years ago.
I ombre'd my hair about a year or so ago (when I was done with the pink) and have found it to be so easy and perfect for moms that I've been referring to it as the mom-bre. (I first heard the term out of my friend Nish's mouth and I thought, That is the perfect term for this minute's hairstyle.)
Essentially ombre hair - mombre hair - is dark on the top fading to bleached ends. It looks like you just have very long roots (like, years long) but it's intentional! Perrrrrrfect for the frazzled or lazy or budget conscious momma, because the upkeep is eh, whenever.
Celeb moms who do the mombre well:
Personally, I find the darker color up top to be more flattering to my skin tone, but I like the pop of blonde at the ends. Plus I was starting to feel like my heavily-highlighted-every-6-weeks 'do looked overprocessed and dated.
Probably in a few years, the mombre will look weird and dated. But it's just hair, you know? Tells time like the calendar.