What Causes Tissue Paper Like Discharge During Periods?

Hi, I just passed what I can only explain looks like tissue paper during my period. I looked it up online and saw a picture of dicidual cast, looking the same as what I just passed.
what is it
as far as I know, I'm not preganant. Am not on any contraceptive either. Am married with one child aged 6.am 41 years old.