“First Look”

My friend has two daughters, both pretty trendy. My friend is a great go-to party planner and she planned both weddings. The older got married 5-6 years ago and the younger like 1.5 years ago. For the last wedding, my friend had referred to their “first look” as she was running thru their plans when we were talking about the wedding. I didn’t give it much thought but now I see it’s referred to on here as a “thing”, like with a name. What, exactly, does it mean? And when did this start? Both daughters were pretty into current wedding trends and I don’t remember this for her older daughter (or anyone else).