The word republic has many meanings - but they can probably be reduced to two. The first simply means a political order in which there is no king or queen at its apex. The Romans who invented the term res publica (public matter) were adamantly opposed to the idea of having a king. Julius Caesar was assassinated because it was believed he wished to make himself king. The second describes a political system composed by individuals motivated by an idea of virtue and by a series of institutional arrangements through which power is divided so it is not concentrated in the hands of an individual.
History
Citation
Melleuish, G. C. (2016). Public won't back a 'politicians' republic', so Turnbull needs to offer a better model. The Conversation, 19 December 1-3.