In the DICOM standard, application context is defined as "the set of application service elements, related options, and any other information necessary for the interworking of Application Entities on an Association; in particular [the application context] specifies the DIMSE Protocol used by the application layer"

In practice, the application context negotiated between DICOM AEs is always DICOM 3.0 (1.2.840.10008.3.1.1.1). The application context is always specified as one of the parameters during negotiation of a DICOM association, and must be specified in a device's DICOM conformance statement.

If there ever is going to be a DICOM 4.0, this is likely to be updated.