The Gemara in Berachos 24b says that שוק באשה ערוה. Therefore it is really important to know what the Gemara means when it says שוק. In modern Hebrew it means the thighs and in fact that is what the Mishna Berura holds, he writes that שוק means the area above the knee.
The Chazon Ish however, disagrees based on a Mishna in Ohalos (8:3) which seems to clearly imply that the שוק is below the knee.
This has a tremendous נ"מ. If שוק is below the knee then a woman would need to cover the area from the knee to the ankle the same way she covers her thighs. Just like stockings/socks is not a good covering for the thighs it should not be for the calves either.
Interestingly enough the Chazon Ish (or other poskim that I saw) does not quote an explicit Gemara in Erchin 19b(that we recently learned in Amud Yomi).
The Gemara in Erchin is discussing what is the definition of רגל. The Gemara tries to bring a proof from Chalitza that you can do Chalitza up to the knee that רגל is up to the knee. The Gemara answers that by חליצה it says מעל רגלו and therefore up to the knee is above the רגל. The Gemara then asks if so what about above the knee? The Gemara answers that above the knee is מעל דמעל. The gemara then asks that from the ankle to the knee should already be מעל דמעל and the Gemara calls the area from the ankles to the knee שקא and therefore from the ankle to the knee should be considered מעל דמעל as well. The gemara answers that the ankle doesn't count (עיי"ש) and therefore the whole are from the foot until the knee is considered מעל רגלו.
We see black on white that the Gemara calls the area from the ankle to the knee שוק.
The bottom line is as the Chazon ish himself says, even the most pious women are not מחמיר to consider from the ankle to the knee שוק and therefore we need to say that שוק means different things in different contexts.