I know that there are some symbols that are frequently used for certain variables. For example, $n$ is commonly used to denote some quantity etc...
So, what if $n$ has already been used? Can we use just any symbol? Like $\psi$, $\lambda$, $\omega$, etc...
By the way, I'm in high school; I'm not too familiar with the world of math.
Certain symbols are traditional in mathematics (e.g., $n$ for natural number, $q$ for rational number, $x$ for real number, $z$ for complex number, $\theta$ for angle, $\phi$ for the golden mean, $e$ for the base of natural logarithms, $\pi$ for the ratio of a circle's circumference to its diameter, $\lambda$ for eigenvalue, $i$ for square root of $-1$, $\omega$ for complex cube root of unity, etc.), but, as long as you define it, the choice of symbol is your prerogative as the author.