What Are Tags?

i've started thinking about, what even are tags? Why do i even have tags? And i came up with 't like, five kind of key reasons why tags exist. The first is certainly necessary conditions. So if a task is tagged in a certain way, unless that tags condition is true, i can't do it. Am, and then the second category, sort of like optional conditions. This is more like, ah, not a constraint, necessarily. It's just when i'm in that sort of mind set, i can go digging and see what things i could do. I want something that i can do when i basically only have like, a phone in one hand.