SCU and SCP describe roles for a particular DICOM service. In plain language, one side asks for or initiates the service; the other side provides or responds to it. The same product may play different roles for different services.
Compare the service, not the acronym alone
Start with the workflow action: store an image, query for studies, retrieve priors, create a worklist entry, or report completion. Then verify the service, role, SOP class, transfer syntax, and relevant conditions on both sides.
Watch for false symmetry
Two documents may both mention the same service while describing the same role, different optional behavior, or support limited to a particular application entity. A good comparison preserves those details instead of collapsing them into a single yes or no.