I also didn't bother to look up the meanings of equality, fairness or diversity. But those words are fairly straightforward and one learns them when one learns English.
"Equity" is one where the implied usage in corporate settings is pretty confusing given the standard meaning (see next para) of that word. So if my corporate bosses and HR are going to use that word, it is on them to educate and address the confusion of the audience.
Dictionary definitions of equity: "the quality of being fair and impartial", "the value of the shares issued by a company". Assuming it's the former, what does my HR even mean when they say we should be "fair and impartial"? On the one hand, that's a given, like saying "we should obey all the laws". On the other hand, if we are not being fair and impartial, then HR should lay out specific ways in which we are not and also the specific remedies.