Bit Depth

Bit Depth is the amount of bits that is used to determine the colour, or “colour component” (grum.wordpress.com) of a single pixel, which is otherwise known as BPP (Bits Per Pixel) when discussed as a pixel, but when referred to a certain colour component “it is known as Bits Per Sample (BPS).” When it comes to bit monochrome, black and white are the only colours that characterize a single pixel, and when an image is in monochrome it is other known as a Binary Image, due to the two colours. Monochrome images are most likely used for printers and fax machines etc. as the pixels in most digital screens always include colour, also they are usually stored in a bitmap format as a raster image, which means that the files are rather small.
High colour is where the image information allows pixels to include two bytes. There are different amounts of bits when it comes to high colour, for example 15 and 16 bit high colour, and the difference is 16 bit high colour has the colour green as their main colour due to the operators eye being more sensitive to the colour green. On the other hand 15 bit high colour uses blue, green and red, with one bit in another channel. 
There are overall “256 different intensity values for each primary colour” (cambridgeincolour.com), which works out to 8 bits per channel, which is usually used in digital cameras. The name for having 256 colours available in 8 BPP (Bits Per Pixel) is VGA, and is mostly used for JPEGs and TIFFs. When there are all of the three RGB colours and they all add up to 256, and due to having 8 bits per channel this is a true colour. Because of the amount of colours true colour is used in graphics or images being processed.