My one tooth gets really sensitive to cold when I drink liquids. What does this mean??

I used my finger to place water on my tooth to see where the sensitivity is and it is right on the gumline.

It's very possible that your gum has receded or the enamel or cementum of your tooth has worn to where the sensitive part of the tooth is exposed, and this can make your tooth sensitive to cold. See your dentist who will be able to determine if it's simply gum recession or a true cavity.

If the tooth is also sensitive to heat, that's more serious and indicates that there is usually deep decay.

zuzu xx