I do not know what the Q stands for with the sizing. What I can tell you is that I bought my regular size Large and the Waders fit. The booty is larger than my foot, but with thick socks and in a size larger wading boot 9.5 women's work great. I have worn these in the river and have not gotten wet. They are well made and comfortable.
I'm pretty sure Q stands for Queen, as in extra width for those a little more endowed.