A red, enflamed bulb of skin that grows over the side of your toenail. Usually considerably annoying and mildly painful until it is removed by a doctor. What the doctor will do is anesthetize your toe and cut away part of the toenail, and that part will have to grow back over several months.
Ingrown toenail is caused by clipping your toenail too deep on the sides, or by chewing your toenails. Don't do it unless you want a trip to the doctor.
You will know you have an ingrown toenail when the toe starts to bother you around 5-7 days after you caused the trauma. It will CONTINUE TO GROW until you get it removed, it will never go away. It will develop scab tissue over the enflamed part to protect itself.
Johnny clipped his toenails too close to the skin on the sides, and several months later he had an ingrown toenail. His complaint was, "Then why do they make the toenail clippers curved on the sides?"
Betsy developed the unfortunate habit of chewing on her toenails, and several weeks later she had 2 ingrown toenails.