Accessible data visualization means a chart conveys its meaning through more than color and shape alone: sufficient contrast between data series, patterns or labels in addition to color coding, and an accessible data table or text summary offered as an alternative for anyone using a screen reader, since even a perfectly labeled chart image cannot be interpreted by assistive technology on its own.
This matters increasingly as dashboards and data-heavy interfaces become standard in business software, where a color-only legend distinguishing five data series can be genuinely unusable for a user with a color vision deficiency, not just mildly inconvenient.