In TeXForm#
TeXForm parses this entry as a character leaf mapped to U+039E (GREEK CAPITAL LETTER XI).
\bbalpha\bbbeta\bbchi\bbdelta\bbDelta\bbdotlessi\bbdotlessj\bbepsilon\bbeta\bbgamma\bbGamma\txtbfbbXi
\txtbfbbXiSymbol
The Ξ symbol (Greek capital letter xi, U+039E), written as \txtbfbbXi in LaTeX text mode.