Bitcoin faucets are a reward system, in the form of a website or app, that dispenses rewards in the form of a satoshi, which is a hundredth of a millionth BTC, for visitors to claim in exchange for completing a captcha or task as described by the website.
There are also faucets that dispense alternative cryptocurrencies.
Rewards are dispensed at various predetermined intervals of time. Faucets usually give fractions of a bitcoin, but the amount will typically fluctuate according to the value of bitcoin.