(1) A storehouse of electronic data.  See 
GitHub.
(2) A database of information about application software that includes author, data elements, inputs, processes, outputs and interrelationships.
(3) A database of digital certificate information.  The repository is maintained by the certification authority (CA) and is queried to find out if a certificate is valid, has expired or has been revoked.  See 
CA and 
PKI.