Chakra is
Naruto's (anime series) answer to other roleplaying games' or shows' mana. The theory states that
chakra is an energy that is created within the human body and released through tiny holes in your skin known as chakra holes that enables you to apply near-magic techniques into fighting, such as
boosting your kicks and punches, improving movement speed, agility, and even manipulate the environments to create wind, energy thrusts, walk on vertical surfaces etc etc etc...
Naruto has an exceptionally high chakra production within his body in addition to being able to draw extra -special- chakra from a
fox demon
sealed within his body to perform special moves and fighting techniques.