1informal, humorous, historical (A nickname for) the Home Guard.
2informal, humorous (A nickname for) any military force likened to the Home Guard as portrayed in the television series Dad's Army, especially one whose members are elderly, inexperienced, or poorly equipped.
3informal, humorous In extended use: (a nickname for) any group of people likened to the Home Guard unit portrayed in the television series Dad's Army ; specifically (a) depreciative a political organization, sports team, etc., whose members are regarded as inept or too old to be effective; (b) a group of (especially elderly) amateurs or volunteers brought together to pursue a particular goal.
Characteristic or reminiscent of the television series Dad's Army, especially in involving a military force whose members are elderly, inexperienced, or poorly equipped. Also of a sports team: made up of players regarded as being past their prime.
1970s. From Dad's Army, the name of a British television comedy series set in a fictional Home Guard unit during the Second World War from the genitive of dad + army.