Add terms related to in-person proofing with USPS (#434)

_articles/glossary.md

@@ -194,6 +194,11 @@ To differentiate, we could say:
 
 > The user proofed their identity to complete identity verification.
 
+### IVS
+**Identity Verification Services**
+
+This refers to part of the Identity and Access Management portfolio of the U.S. Postal Service.
+
 ### LOA
 **Level of Assurance**
 
@@ -264,6 +269,11 @@ Source: [CNSSI-4009](https://www.ncsc.gov/nittf/docs/CNSSI-4009_National_Informa
 
 An entity that relies upon the Subscriber's token and credentials or a Verifier's assertion of a Claimant’s identity, typically to process a transaction or grant access to information or a system. Source: SP 800-63
 
+### RSS
+**Retail Systems Software**
+
+This is point of service software used by the U.S. Postal Service.
+
 ### SAML
 **Security Assertion Markup Language**