Both are classified as indirect costs; that is, they cannot be directly applied to any specific contract. The difference is that G&A refers to that portion of your indirect costs that apply to your whole operation; whereas overhead applies to a portion of your operation. Examples of overhead are: utilities, rent, added insurance, leased equipment. All apply to a specific function or cost within your organization. General liability insurance, legal costs and state/federal taxes, for example, would be classified as G&A.