AES is a symmetric key encryption cipher used to secure large chunks of data at rest. AES-256 is AES implemented with a 256-bit key size, which is its strongest setting.  AES is approved by NIST, and the US government secures its top secret data with AES-256. This has led many VPN services that use AES-256 to describe their encryption in terms such as “military grade.” AES-256 is, indeed, very secure, but it is only one of the components required to ensure a VPN connection is secure.