The concept of whether a product, service, or space can be used by as broad an audience as possible, which differs from general usability by focusing on providing an equivalent user experience to people with disabilities. Factors that make up accessibility include visual, auditory, and mobility components, and the ability of a product, service, or space to interface or be used with assistive technology (such as a screen reader or mobility aids).
Citation: Center for Scientific Collaboration and Community Engagement. (2021) CSCCE Glossary: Inclusive Language in Community Building. Woodley, Pratt, Bakker, Bertipaglia, Dow, El Zein, Kuwana, Lower, Roca, and Santistevan doi: 10.5281/zenodo.5718783
Specifically, when thinking about virtual environments, accessibility considerations include providing closed captioning and/or subtitles, ensuring the platforms you use are screen reader compatible, offering asynchronous content, and ensuring participants have multiple ways that they can take part (e.g., text-based messaging and opportunities to connect one-on-one or in small groups).
Further reading: Ensuring Virtual Events are Accessible for All, by RespectAbility: Lauren Appelbaum and Eric Ascher
Citation: Center for Scientific Collaboration and Community Engagement. (2022) CSCCE Glossary: Virtual Events. Pratt, Woodley, Ainsworth, Carter, Crall, Elkins, Gauthier, Ihle, Kornahrens, Martinic, Santistevan, Shaikh, Sidik, and Wyatt doi: 10.5281/zenodo.6608609