A general meeting of a company is a meeting of all members of a company (this usually means shareholders), and, in the UK, is simply called an general meeting unless it is the annual general meeting AGM A general may be called at any time. A general meeting is therefore called when a decision needs to be made that cannot wait for the next AGM.
In some countries a meeting needs to be designated an extraordinary general meeting in order to pass certain resolutions. This is no longer required in the UK, although some resolutions (e.g. winding up a company) still require more than a simple majority to pass, they may be passed at any general meeting, including the AGM.
An general meeting is called by the directors of a company. Shareholders with a sufficient stake may force a meeting.
Reasons for calling a general meeting include: