What is the meaning of Variable?

In mathematics, a variable is a symbol, typically a letter, that represents a quantity that can change or take on different values.

Explantation: Define with examples (e.g., $x$ in $2x + 5 = 11$). Explain its role in algebraic equations, functions, and formulas. Differentiate from constants. Discuss independent and dependent variables in the context of functions or experiments.