A service medal is a military award generally of the lowest degree. A service medal is awarded to a member of the military who joins the military, or is already serving, during a designated time period. No other requirement is needed to obtain the service medal other than a person must simply be a member of the armed forces.
Campaign medals are similar to service medals (and are sometimes even referred to as service medals), however the main difference is that a campaign medal is awarded to a military member who participates in a military operation whereas a service medal is blanket awarded to everyone in the military regardless of campaign credit.
An example of a service medal currently issued by the United States armed forces is the National Defense Service Medal which is presently automatically awarded to a service member upon joining the military usually after completion of basic training.
The Global War on Terrorism Service Medal is not a "blanket" service medal because it requires actual service rendered in support of the Global War on Terrorism.
