20 CFR §210.2

Service means a period of time for which an employee receives payment from a railroad employer for the performance of work; or a period of time for which an employee receives compensation which is paid for time lost as an employee; or a period of time credited to an employee for creditable military service as defined in part 212 of this chapter. Service shall also include deemed months of service as provided under § 210.3(b) of this chapter and any month in which an employee is credited with compensation under § 211.12 of this chapter based on benefits paid under title VII of the Regional Rail Reorganization Act of 1973.