​Similar sounding terms and acronyms are often at risk of being inadvertently co-mingled or misused. As a public service, permit me to differentiate between four seemingly similar terms that are particularly at risk of incorrectly being used interchangeably:

• Operations & Support (O&S) is a life cycle phase (Ref: DoDI 5000.85, Para 3.15). This phase executes the Product Support Strategy, satisfies materiel readiness and operational support performance requirements including personnel training, and sustains the system over its life cycle, including disposal. The O&S phase begins upon fielding of the first system(s), which may precede IOC, and is based on an MDA-approved PSS. This phase includes two major efforts: sustainment and disposal. The MDA-approved PSS is the basis for the activities conducted during this phase.
   
• Operating & Support (O&S) is a life cycle cost category (Ref: September 2020 CAPE Operating and Support Cost-Estimating Guide). Life-cycle cost is defined as the sum of four major cost categories: (1) research and development costs; (2) investment costs, consisting of procurement and military construction costs; (3) O&S costs; and (4) disposal costs. (para 2.1 )  At the broadest level, O&S costs consist of all sustainment costs incurred from the initial system deployment through the end of system operations. This would include all costs of operating, maintaining, and supporting a fielded system. Specifically, this consists of the costs (organic (government civilian and military) and contractor) of personnel, equipment, supplies, software, and services associated with operating, modifying, maintaining, supplying, and otherwise supporting a system in the DoD inventory. These costs include those associated with the system-specific training of personnel necessary to support the system. (Para 2.3)

• Operations & Sustainment (O&S) is a new term used in the Adaptive Acquisition Framework graphic in the yellow box for the top three pathways (UCA, MTA, MCA) (Ref: DoDI 5000.02, Figure 1 and DoDI 5000.85, Figure 1). We have requested clarification as to whether this is intended to be a phase, an activity, a deliverable.
   
• Operation & Maintenance (O&M) is an appropriation (Ref: DoD 7000.14-R Financial Management Regulation (FMR)). Expenses incurred in continuing operations and current services are budgeted in the O&M appropriations. (Vol 2A, Ch 1, Para 010211.B.3.) O&M is a direct appropriations which may be used to start or fund readiness costs not related to the specific Defense Working Capital Fund (DWCF) activity operating mission. Direct appropriations may also be used to increase the size of or replace significant losses in a DWCF activity. (Vol 3, Ch 19, Para 190202.D.)