You will find the terms offset and or displacement in some of the APIs. For example, the Retrieve Data Queue Message (QMHRDQM) API uses offset; the List Objects (QUSLOBJ) API uses displacement.
An offset is the distance from the beginning of an object (user spaces and receiver variables) to the beginning of a particular field. However, a displacement is the distance from the beginning of a specific record, block, or structure to the beginning of a particular field.