UNI is a so called government token. Owner of the UNI token allows you to have a say in the governance of the Uniswap platform. When new developments and structural changes are put forward, you have a right to vote on them, proportional to the amount of UNI tokens that you own. There are one billion UNI tokens, of which 150 million were airdropped in 2020 to anyone who had used the platform in the past.