It's a legal term - https://en.wikipedia.org/wiki/Discovery_(law). Most countries/industries have some kind of regulation around data storage and retention for exactly this purpose.
The entire point of end-to-end encryption is to prevent this from being automated and abused by either the legal system or the company. Requiring a warrant to access the secret key on the user device reduces the risk of mass surveillance. Metadata (access logs) remain in clear text and can still be used to help authorities identify nefarious activity.
