No matter how bad of a beating you take from anyone of any power level there is one thing that will always bring you back from the brink of death. It'll give you the energy to throw yourself back into the fray and possibly take yet another beating, that thing of course is the magic green Senzu Bean!
The Senzu Bean itself is grown up in a tower miles above grown level by Korin; a white furred "man-cat" with a mean looking walking stick, they are said to taste like celery. Besides the bean healing people's injuries, the bean can actually be used as a food ration which keeps a human full for up to 10 days (although judging by a Saiyan
's appitite, it might not keep them full for quite as long). The bean does not increase the strength of the user, rather it restores their energy/ki. A Saiyan may be more powerful after being restored by a Senzu Bean, but that is because Saiyans naturally become stronger after recovering from severe damage.
Although it can heal any battle injuries the bean can not heal illness or any kind of ailment.
The Senzu Bean has been known to cure fatal wounds and actually regrow limbs and flesh. Examples of this are when Yamcha
has a hole right through the torso and after eating the bean the hole was healed and he was at perfect health. Gohan
also ate one which aided in him growing back a severed arm.
Senzu Beans have been featured in most of the Dragon Ball Z
games as items to heal your health in battle, or between battles.