How about thinking in terms of being able to afford food?

If there's a small minority of the population that are so rich that they cannot meaningfully even spend their money (e.g. billionaires) and at the same time there's a sizeable percentage that cannot afford to eat regularly, then that's wealth inequality.

It's not so much about making everyone equal, but ensuring that almost everyone can provide for their basic needs (e.g. housing, food, medicine).