All expenditures incurred by the department of central government in charge of defence, including military personnel, military equipment and weapons, military structures such as airfields, docks, buildings and hospitals, transport, communication, as well as overseas military bases, missions, and peacekeeping forces.
Data on defense spending from governments are often incomplete and unreliable. Even in countries where parliaments vigilantly review government budgets and spending, defense spending and trade in arms often do not receive close scrutiny. (World Bank)
Typical difficulties with official data:
may vary widely depending upon the coverage: active army forces, reserves and auxiliary forces, paramilitary forces, police, civil defence, armed forces personnel pensions, social security contributions, etc.
data may omit parts of military spending, disguise financing through extra budgetary accounts, omit military assistance or secret military equipment imports.
current military spending is likely to be reported, but capital spending not so likely.