The iOS 9 Trust Store contains three categories of certificates:

Trusted root certificates are used to establish a chain of trust that's used to verify other certificates signed by the trusted roots, for example to establish a secure connection to a web server. When IT administrators create Configuration Profiles for iPhone, iPad, or iPod touch, they don't need to include these trusted root certificates.

Always Ask certificates are untrusted but not blocked. When one of these certificates is used, you'll be prompted to choose whether or not to trust it.

Blocked certificates are believed to be compromised and will never be trusted.

This article lists the certificate trust policies for iOS, and is updated when changes are made to the certificate list. You can find the version of the Trust Store installed on your iOS device by tapping Settings > General > About. Scroll down to the bottom of the list to see the Trust Store version.

This article lists the certificates for iOS Trust Store version 2015111600, which is current for iOS 9 and later.