added simple credit refund definition to glossary

added simple credit refund definition

specification/glossary.md

@@ -64,6 +64,10 @@ A feature of [*commitment discounts*](#glossary:commitment-discount) that may fu
 
 The agreed-upon unit price for a single [Pricing Unit](#pricingunit) of the associated SKU, inclusive of negotiated discounts, if present, and exclusive of any other discounts. This price is denominated in the [Billing Currency](#glossary:billingcurrency).
 
+<a name="glossary:credit"><b>Credit</b></a>
+
+A positive balance or amount remaining for free/discounted usage of services that is provided independently of other charges.
+
 <a name="glossary:dimension"><b>Dimension</b></a>
 
 A specification-defined categorical attribute that provides context or categorization to billing data.
@@ -136,6 +140,10 @@ A comprehensive list of prices offered by a provider.
 
 An entity that made internal or 3rd party resources and/or services available for purchase.
 
+<a name="glossary:refund"><b>Refund</b></a>
+
+A return/repayment of funds that have previously been charged.
+
 <a name="glossary:resource"><b>Resource</b></a>
 
 A unique component that incurs a charge.