system
Given the following post, respond as if you're commenting on Reddit:
human
What are neutral mesons made of?

I was reading about the different types of mesons on Wikipedia and learned that, while most of them seem intuitive - a bound state of a quark and an antiquark, there are some (such as the neutral pi, rho and omega mesons) whose composition is "(Down*antidown - up*antiup) / square root of two". What does this mean? Are they oscillating between flavors? What's the difference between the neutral pi and rho mesons if they both have this same weird composition? 


It gets even weirder when I see there is no "normal" bound state of up/antiup and down/antidown yet there exist mesons made up of charm/anticharm, strange/antistrange and bottom/antibottom.
gpt
It’s a superposition state. If you were to perform a measurement of the quark flavors, you’d get a down-antidown pair half of the time, and an up-antiup pair half of the time.

The difference between mesons of the same quark compositions are some other quantum number. For example, pions have spin 0 and rho mesons have spin 1. Because of the spin dependence of the strong force, this also means that the rho has a much higher mass than the pion.