Consent expression

The form in which consent was expressed: explicit opt-in, signed opt-in, witnessed opt-in, biometric opt-in, opt-out, or implied. IMPORTANT cross-reference: opt-in-biometric refers to the capture method (for example, fingerprint as signature), not to the data category. Processing biometric data is expressed via personal_data_categories (a URI from dpv-pd or equivalent).

https://publicschema.org/consent_expression