"Blanket consent" refers to giving permission or approval in a broad or general way, without specifying the exact details or circumstances. It means agreeing to something without knowing all the specific details beforehand. Full definition
The efforts paid off: Under the revised legislation, scientists will have access to any data derived from patients and study subjects who give blanket consent for research. (sciencemag.org)
(d) You must not use blanket consent forms authorizing the release of employee testing information. (transportation.gov)
In research on attitudes, Caulfield has noticed a trend: clinical researchers, patient participants, privacy experts and the general public disagree about whether consent should be necessary for each new use of donated tissue or whether blanket consent will do. (scientificamerican.com)