The names of function arguments are arbitrary. Think of them as placeholders within the scope of the function that substitute visually for the input values that will get crunched while the code is running. They can be named anything, so just use something that makes sense to you (and anyone else who might have to read your code later) within the context of the function.
For example in pseudocode not tied to any particular language:
define function foo(value)
multiply value by 3
In this example, the function is named foo, takes (value) as an input, and multiplies the input by 3. I fed it a 9 when invoking the function by putting (9) where it maps to (value) in the original function -- the 9 becomes its argument.
In the example itself, the function argument is named (food) simply because it makes sense within the context of the function -- it's easy to understand at a glance that you're crunching prices of the foods you're stuffing into the function. Strictly speaking, you can rename the argument to (x) or (list) or (your_mom) or anything else you like, so long as it remains consistent throughout the function.