English is not my first language can someone help me understand a post?

What is a common law marriage I just read a post about that and I have no clue what that means?

03
About Anastasiya Belov
Birth: July 14
On Moms.com since: Feb 24, 2014
I am stay at home mother who just recently moved to the US from the Russia. I came here to go school and met my husband. After that we planned a marriage and I moved here in 2009. We have 2 small children and I am a stay at home mom but I do work from home