The Directive provides definitions of key terms. 'Public-interest entities' comprise undertakings governed by Member State law whose transferable securities are admitted to trading on a regulated market; credit institutions as defined in Directive 2006/48/EC (excluding those in Article 2 of that Directive); insurance undertakings within Council Directive 91/674/EEC; and undertakings designated by Member States for significant public relevance. It also defines 'participating interest', 'related party' (per international accounting standards under Regulation (EC) No 1606/2002), 'fixed assets', and corporate relationships including 'parent', 'subsidiary', 'group', 'affiliated' and 'associated' undertakings (with a 20% voting-rights presumption for significant influence).

The Directive defines financial and measurement terms and reporting concepts: 'net turnover' with sector-specific definitions for insurance and credit institutions and for entities under Article 40a(1); 'purchase price'; 'production cost' (permitting a reasonable proportion of attributable overheads but excluding distribution costs); 'value adjustment'; 'material'; 'sustainability matters' and 'sustainability reporting'; 'key intangible resources'; 'investment undertakings' and 'financial holding undertakings'; and 'independent assurance services provider' as a conformity assessment body accredited under Regulation (EC) No 765/2008.