The act of pleasuring oneself sexually. This is done by men and women. It is nothing to be ashamed of everyone does it, just besure your alone and not in public. Boys need to clean up afterwards.
Masturbation is the act of sexual pleasuring yourself, by touch, rubbing or whatever method you can find that gets you to sexual completion, orgasm for women & Ejaculation for males
Some religions prohibit or discourage it, but it is not harmful to the body if done safely and with some moderation.
Masturbation does take time & energy and too much masturbation can cause rashes & infections, Urinary tract infections and other complications. Occasional masturbation with lubricant and good hygiene before and after should cause no physical damage.
The psychological implications of masturbation are as complicated "for" as "against". lack of sexual release can cause obsession and obsessive need for stimulation can create psychological problems so again we are back to normal, occasional Masturbation is just that; NORMAL human behavior, that we share with many primates and other mammals. Chimps, dogs and dolphins all masturbate as part of their normal sexuality.