A piece of software that anyone can host on the internet which allows you and others to watch YouTube without loading their original page full of ads and anti-features, whilst also allowing you to have a certain level of anonymity and improved privacy.
(the anonymity comes from collective anonymity, where you’re harder to make out in the crowd, as YouTube only sees a bunch of people watching a bunch of random videos, but not who is watching)
They will actually, as they’re looking for specific things to be blocked/altered using JavaScript that is easily affected by enabling certain custom lists. In case you don’t believe me, you can look on uBO’s official statement regarding this.