Harmonised Standards
Technical standards adopted by a European Standards Organisation and referenced in the Official Journal of the EU. Conformance with a harmonised standard creates a 'presumption of conformity' with the corresponding EAA requirements. For ICT services, the operative standard is EN 301 549.
Official EU-endorsed technical standards. Follow one and you're assumed to meet the matching legal requirements.
Under Article 15 of the EAA, products and services that conform to harmonised standards (or parts thereof) whose references have been published in the OJEU are presumed to be in conformity with the corresponding accessibility requirements. EN 301 549 v3.2.1 is the current reference for ICT; updates to align with WCAG 2.2 and EAA-specific service requirements are in progress at ETSI/CEN/CENELEC.
Why this matters
Harmonised standards are how operators prove EAA compliance in practice. The directive sets functional requirements; the harmonised standard gives the testable detail. EN 301 549 maps WCAG 2.1 Level AA (and increasingly 2.2) plus additional requirements for software, hardware, documentation, and support services.