The correct term for the tail dropping is actually Autotomy.

A lot of reptile species have a defence mechanism being their tail, they can drop their tail if they feel threatened or the tail is grabbed so whilst the tail is still wriggling the reptile can escape the danger.
This can occur by;

• tail being grabbed

• being bullied by other geckos sharing a tank

• stress/fear

• infections

• Skin issues and retained skin on the tail

• Bacterial, fungal, or protozoan infections

• Abscess or swelling in the area

These can all cause the gecko to drop the tail.

 

If the tail is dropped it Will regenerate it won’t take the same form nor pattern it tends to be smooth in feeling a lot bigger then what it was and normally a tad shorter. They are designed to do this, with special connective tissue in the tail that creates a "weak spot" where the tail breaks off readily. If a gecko drops its tail, the blood vessels to the tail will constrict, so very little blood loss occurs.

 

If this occurs within the Leopard gecko you keep there’s a few things you can do to de stress them whilst they recover;

• Use paper towels for substrate. Loose substrates can get into the wound and lead to infections. Change the paper towels often to keep the environment clean.

• Isolate a gecko with tail loss from other geckos, as other geckos may bully a gecko that has dropped its tail.

• Watch the stump for signs of infection and consult your vet if there is any swelling, redness or oozing at the site of tail loss.

• Evaluate your temperatures and humidity to make sure the environment is ideal. Tail loss and re-growth is stressful and you want to make sure conditions are ideal for your gecko.

• Make sure the gecko is eating well; you can ramp up the amount you normally feed a bit since tail loss is stressful and also means loss of the gecko's fat stores. However, make food that is not eaten (that are not inside a bowl) are not eaten within about 15 minutes are removed from the tank.