What is a dot?

[mock1328]

aura check says I'm missing some dot, but what is it and when/why it's used? Searching in AUR reveals a lot of results, but the only entries that says dot-git or dot-bin are about some firefox fork and I highly doubt it's the right dot

[mock1328]

Found it in a PKGBUILD as optdep by trial-and-error. It's graphviz. I wish this was stated more clear in a helping message