According to Wikipedia:
The PowerShot products are a line of consumer and prosumer grade digital cameras, launched by Canon in 1995. The PowerShot line has been successful for Canon, and is one of the best-selling digital camera lines worldwide.
The Canon PowerShot G is a series of digital cameras released by Canon. The G series cameras are Canon's flagship models aimed at prosumer photography enthusiasts desiring more flexibility than a point-and-shoot without the bulk of a digital single-lens reflex camera.
The G series offers features such as the use of a lithium-ion battery, a flip-out-and-twist LCD (all models except G7, G9 and G10 which have a fixed screen), Raw image format capture (all models except G7), a lens with a wider maximum aperture than standard PowerShot models, remote capture (except G11), and faster electronics. The range also includes a hot shoe for an external flashgun, including Canon's EX range.