It is good to know that the word “gusset” is not only used for pantyhose. It simply means a piece of material sewn into a structure to create a proper fit. You can find gussets used in shirts, bags, and so on. Let me try to answer the question – what is a gusset?
Pantyhose gusset brings some debate. I may find the courage to address it at some point. Let’s just say that some people think it is there in order to be able to wear pantyhose without additional underwear.
But from brands like Fiore we see a strange thing – they only have gussets in size M and L, but not in size S. It’s there for the fit. Some other brands may have synthetic gussets, also to create a proper fit.
Somehow larger the size, more need is there for additional fabric in between, or maybe it’s just a side effect of production limitations. A Polish lady told me that Marilyn hosiery brand, for example, finally found a way to create plus size pantyhose without having to use a large gusset.
Our local yoga pants brand for example states that they add gussets to their pants in order to increase comfort and mobility of pants that will never ride up. They openly say that it prevents the embarrassing problem when the seam of the pants cuts in between the women’s legs and creates a visible cleft.

Inserting gussets is a time consuming procedure, so you may notice that cheaper brands may not have it. You may be interested to see how many pantyhose patents there are on the internet trying to scheme around this.
Opinions? I am sure you’ll have some!
Some Comments from the Forum:
by CJ, TightsFashionUK
What is a gusset?
“A gusset makes for a much better fit as well as ensuring there is no seam directly over sensitive areas. It is no accident that all quality brands include a gusset … as indeed do lesser brands on their premium styles. Gussets tend to be omitted only to save money in production.”