What does a quark content that is divided by a square root-mean?

[swampwiz]

I was looking at the Wikipedia article on mesons, which has a table of all the observed particles in which one of the columns is the quark content. For most particles, it is a simple set of 2 quarks, but sometimes is shows a more complicate formula, including division by the square-root of some small number like 2, 3 or 6.

https://en.wikipedia.org/wiki/Meson

 

[mfb]

It's a superposition of the listed contents.

 

[Orodruin]

Those would be the cases when the meson is a quantum mechanical linear superposition of the flavor states. The numbers represent the amplitude of each flavor combination. For example, if the meson contains $u\bar u/\sqrt{2}$ it has a probability 1/2 to be u-quarks.