Where are Expenditure Type Classes created and/or managed?

Looking at our SLA rules and curious how we know the codes for Expenditure Type Classes and where they are created/managed. In one example, there is an existing Journal Line Rule that indicates - "Expenditure Type Class" = ER - how do we find out what the code "ER" is and a list of the other possible options? Can new values be created or old values ended?

Thanks in advance,
Jon