In an equation "x" is the value assigned to one of the unknown quantities in the equation. (example: y= mx+b).
X is often used to describe any unknown thing, as in x-ray which were named this because the nature of the ray was initially unknown.
Chat with our AI personalities
If you're talking about Roman Numerals, 10. If you're talking about something else, it's unknown; that's why they used a variable to represent it. (It may be possible to find the value of the variable, but you'd have to give a lot more details.)
"X" as well as other letters are used in algebra as a variable, meaning either that they can have any value, or that their value is initially unknown.