I get this when clicking on an type in Phtoshop cc21. What is it?
When there is an alternate glyph for a character, it allows you to swap it on the fly. The alternates are available when they are built into the typeface by the designer, and might include superscript, subscript, small caps, real fractions, and more. If you don't want to see it, you can turn it off as mentioned by @c.pfaffenbichler.