X; the letter X
Refers to the letter X itself, as in the alphabet, or as a symbol.
Please sign at the X on this document.
unknown quantity; an unknown
Used in mathematics or general contexts to represent an unknown value, person, or factor.
Find the value of X in the equation.
The letter X in the alphabet is read as 'ekkusu'.
彼の実力はまだＸだ。
His true ability is still an unknown.