What does this notation mean? ex: 1s:A, 1s:E

[vancouver_water]

From this paper, on page 2: https://arxiv.org/pdf/1606.03488.pdf.

In the absence of spin, these levels are split by valley-orbit terms and, in increasing
energy, are labelled according to 1s:A (one level), 1s:T₂ (three levels) and 1s:E (two levels).

I know the spectroscopic notation part, but what is the meaning of the symbol after the colon?

 

[mjc123]

A, E and T₂ are symmetry labels in tetrahedral symmetry. They are singly, doubly and triply degenerate respectively.