There is only one file type that uses the .KEYSTORE extension:
Java Keystore File
Security file commonly used by (IDEs), such as Eclipse and Unity, to verify application developers; stores a set of cryptographic keys or certificates in the binary Java Key Store (JKS) format.
A KEYSTORE file is used for several security purposes. It can be used to identify the author of an Android app during a build and when publishing to Google Play or in SSL encryption.
Since a KEYSTORE file contains valuable data, the file is encrypted and protected by a password to secure the file from unauthorized parties. There is no way to retrieve your KEYSTORE file if you lose it, so be sure to back it up.
NOTE: The KEYSTORE extension is similar to the .JKS extension.
Updated: August 13, 2014