Is it correct to define variables and functions that are more than one character?

Question

Most of the time (at least at my high school student level), we are using variables such as a, b or $\theta$, and functions such as f, g etc...

But would it be possible to use multiple characters ? For example to use triple(x) = 3x instead of f(x) = 2x ?
In my opinion it would enable some things to be much more clear in many situations, here is another example : $$area = width \times height$$ Instead of $a = w \times h$, where you would need to go back in the text to find wha a, w and h are for.

Answer 1

Of course it is possible, and it is done. Some examples: $\log x$, $\sin x$ and the trigonometric functions, $\text{div}$ (divergence operator), $\text{grad}$ (gradient, also $\nabla$), $\det A$ (determinant).

The use of a single character is a matter of economy. You can use whatever notation you like, as long as you explain it if it is not standard.

Answer 2

It is done all the time in computing. It is a major help when reading someone else's program.
We also use subscripts - rather than ($x,y,z$), we might write $(x_1, x_2, x_3)$; then refer to any one of them as $x_i$