Can someone explain the meaning of 'proxied by' in math? or What does 'proxied by' mean in mathematic

Not dumb at all! "Proxied by" is just math-speak for "represented by."

It’s like using a shadow to guess the shape of an object—close enough for the purpose.

In econ, GDP might proxy for standard of living, even though it’s not perfect.

Here’s a short vid explaining it: [link to video].