(od) - outside door
(c/od) - cut-out/fire hydrant
(c/sd) - cut-out smaller door
(ins) or blank - inside unit

An outdoor (od) unit has an outside door. A cut-outdoor (c/od) unit has an outside smaller door. A cut-smaller door (c/sd) unit is near a fire hydrant and less square footage. All outdoor units are ground level, which gives you the ability to load your belongs directly from a vehicle. An inside unit is indoors and will require you to go thorugh an access door, also at ground level.