The term RDL in the context of embarkation is not related to the International Date Line and appears to be specialized terminology that is not standard in the general process of embarkation.
The term RDL, or Reference Datum Line, in the context of embarkation, is unrelated to the International Date Line. The information provided about the International Date Line, which is an arbitrary line on the surface of Earth near longitude ±180° where the date changes by one day, does not correspond to the concept of RDL in embarkation.
As such, without further context on how RDL applies to embarkation, providing an accurate definition is not feasible in this case. Embarkation typically involves the process of boarding a vehicle or ship, but the term RDL is not standard terminology for this process, and may refer to a specific concept within a specialized field or system.