User blog comment:Clarrity/List of ordinals (up to omega^omega)/@comment-108.18.136.209-20180225205355/@comment-34821072-20180225205818

It is the Greek letter omega, and can be copy and pasted in by using the letter itself: ω, or when using it in equations, by using the command \omega surrounded by  and   tags, so that \(\omega\) renders as \(\omega\).