Dry socket is a condition when the blood clot in the extraction is disintegrated and the underlying bone is exposed and dry. It can be quite painful and sometime even more so than a regular toothache.
Normally occurring within the first 2-3 days after extraction, it can sometimes take up to 2 weeks to improve. It can be hard to predict the reason for the same, but if you have been a smoker or have indulged for an extended period in the past, your risk factor is predictably on the higher side.