The COMPLETE keyword causes the referenced definition to belong to the referencing definition, so the referenced definition cannot be referenced by another definition, and can be edited only from the containing referencing definition.
An example is an attribute in an entity, which completely belongs to an entity (and does not belong to another definition), and can be opened only from in the entity definition (you cannot open an attribute definition directly in System Architect’s Explorer, for instance).
Example
DEFINITION "Entity" { PROPERTY "Attributes" { ZOOMABLE EDIT COMPLETE ListOf "Attribute" KEYED BY {"Entity Name":"Name", Name} ASGRID LENGTH 4096 DISPLAY { FORMAT List } } }