What is Transparency?
Transparency is the principle that information about processing should be provided to the data subject. If data subjects make request access to their data, controllers must provide access without undue delay, and in ay event within one month. Controllers must facilitate the exercise of data subject rights, and provide information free of charge.
Controllers also are obliged to provide privacy notices to data subjects, detailing what data will be used and how it will be used.
GDPR, Chapter III, Section 1, Article 12
https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32016R0679&from=EN
Under the GDPR, controllers have an obligation to provide to data subjects, information, in writing or electronic means that is concise, transparent, intelligible and easily accessible form, using clear and plain language.
Transparency / visibility is a foundational principle of Privacy by Design. See Privacy Program Management, Russell Densmore, pages 122.
Transparency is a core principle of the Brasil privacy guidelines. See Lei Geral de Proteção de Dados (LGPD)
http://www.planalto.gov.br/ccivil_03/_Ato2015-2018/2018/Lei/L13709.htm
Art 29 WP Transparency Guidelines