Final answer:
The modifier -25 is used to indicate a significantly, separately identifiable E/M service on the same day as another procedure or service.
Step-by-step explanation:
The modifier used to indicate an Evaluation and Management (E/M) service is a "significantly, separately identifiable service" is modifier -25. This modifier is important in medical billing and coding as it signals to insurance companies that a patient's visit involved a separate E/M service in addition to another procedure or service provided on the same day.
For instance, if a patient comes in for a scheduled procedure and also receives an evaluation for a new complaint, the E/M service for that new complaint may be billed separately with the use of modifier -25, assuming it is a significant and separately identifiable service from the procedure.