Groups in PCoA plot

I have three different groups in my analysis. When I select “show groups” in the PCoA analysis, ellipses are drawn around the sample groups. What do the ellipses actually mean? Are they some kind of confidence ellipses? And how are they calculated?
Thank you!

Dear Vanessa,

Elpises are a viusal marker for grouping the samples. They sorround the samples that share an attribute in the metadata. In ‘Group samples by selected attribute’ dialog you can choose the attribute to be used. Please update if you are using an old version,