What's the difference? The dictionary says both mean socks or stockings. If they really refer to the same thing, what's the regional usage for Mexico and Latin America in general?
In Chile, "medias" has two meanings. The first is not important in this question, is the sport socks, used by both sexes. With a minimal difference are the same as "calcetas".
The second "medias" refers to a type of lingerie, only wear by women. Is a set of panties with legs and which must necessarily be closed on the feet. That is: a trouser with socks, all together, and with "intimate" features. It can be transparent or opaque. In other countries it said "pantimedias".
"Calzas" are outer garment. Are similar to trousers made with thin and flexible material, and with open feet. Are also known as "leggins".
In real life of a man, there is little difference between medias and calzas, the main thing is that enclose a foot and others do not. If they are fully transparent, are medias, and should take more clothes on (unfortunately). But it would be feasible to tell a lady, "qué lindas tus calzas" and she will answer you: "Son medias". It would be nice.
I was hesitating about posting an answer because you are asking for the usage in Mexico specifically, and my Spanish is castilian, but in case it helps and until you get a better and more complete answer...
My understanding is that 'calcetines' is what we use in a daily basis and 'calzas' would designate larger 'socks', like the ones soccer players (among others) may use for sports (calzas deportivas). The word also designates an old fashioned piece of clothing (something between socks and pants. Check this "calzas" and this other one to get an idea of what it was).
Seems they can also be a woman piece of clothing (but in castilian Spanish the word used for them is the anglicism
No idea about the use in Mexico, but I hope this helps until someones posts a more accurate answer.
I learned Spanish while living in Puerto Rico for 5 years. We used "medias" for socks. I live in Dallas, Tx now and the Mexicans call socks "calcetines".
Very interesting how the Spanish language has so many different words for things in different countries. I love learning. So I'll keep my ears open and learn more.
it depends the geographical region of Mexico, for example
Central and south regions: the common term is: calcetines and medias refers to a thin cloth used by women when they wear dresses and it covers both legs
In north region: the common term is medias and it doesn't matter who uses them(women and men)
For example in mexican central region if you say esta zapato me calza bien it means shoes are of your size and you can use them perfectly