Responsible Organization, The carrier that has been designated to "be responsible" to ensure a customer's 800 long distance traffic is routed over the correct carrier.

a company certified by the FCC to access the entire database of nationwide Toll-Free numbers

Short for Responsible Organization. If you have a toll free number in the USA and/or Canada, your toll free number is controlled by a RespOrg. The RespOrg is the organization responsible for controlling and maintaining your toll free number (A.K.A. your toll free service provider).