The difference matters because many US systems were built on unequal footing. School funding is a common example. Many districts rely heavily on local property taxes, so wealthier, whiter neighborhoods can spend more per student. Giving every school the same small grant would be equal, but it would leave the gap in place.
Equity shows up in law and policy. Title I of the Elementary and Secondary Education Act of 1965 sends extra federal money to schools with many low-income students. The Americans with Disabilities Act of 1990 requires reasonable accommodations rather than identical treatment. Both are built on the idea that the same rules can produce unfair results.
The word has become politically contested, often grouped with diversity and inclusion under the label DEI. Critics argue equity means guaranteeing equal results. Supporters, including ARD, use it to mean removing the barriers that keep outcomes tied to race, disability, income or gender. The goal is a system where where a person starts no longer decides where they end up.