The OpenID Connect Core 1.0 specification defines two subject types, public and pairwise.
The public subject type is used to provide "the same sub (subject) value to all Clients" or Relying Parties (RPs), while the pairwise one is meant to provide "a different sub value to each Client, so as not to enable Clients to correlate the End-User's activities without permission".
In other terms, the public subject type is a globally unique persistent identifier, while the pairwise one is targeted to a specific RP.