What is the character obtained with they key sequence Esc,Esc called? On my front end it is not displayed, but there's something there messing up my input. It's a bit annoying when I'm after a $\mu$ but hit the wrong key.
It's what's called an
\[InvisibleComma]. It's useful for those times where you don't want a comma to appear, but you still need it, e.g.
"a[[p\[InvisibleComma]q]]" for a matrix entry.
The third entry uses an
\[InvisibleComma] in between the matrix indices.
The next time you wonder what a symbol is you can at least partially answer it yourself by entering it in a string wrapped in
(this is just before pressing Esc the second time). You would get:
Which is surely helpful in some way. You can also get the help page for the character by entering it directly into the help search box: