First things first, an Organ is a large musical instrument having rows of pipes supplied with air from bellows (nowadays usually electrically powered), and played using a keyboard or by an automatic mechanism. The pipes are generally arranged in ranks of a particular type, each controlled by a stop, and often into larger sets linked to separate keyboards.
A rank is a set of pipes of the same type (shape, material opening etc.) that make the same sound.
Each pipe is tuned to a different note and is controlled by the key of that note so that different ranks sound in unison.
A stop is a mechanism by which a rank is selected to be played when its relative key is pressed.
The terms stop and rank are used pretty much interchangably so unless there is any ambiguity I will use the terms stop, and rank interchangably when what I mean rank so let that be noted.
The organ is usually divided into three or four divisions, being the swell, great and pedal divisions
The pipes of the organ are controlled by a keyboard, the keyboards for the Swell, Solo and Great Divisions.
The pedals that control the Pedal division are laid out like a Piano but are spaced further apart so that they can be played by the feet
There are many different types of pipes that are used, the most common materials for pipes to be made of are Metal and Wood, with metal pipes mostly being made of an alloy of lead and tin,
with the comosition varying depending on the desired sound and also from organ-builder to organ-builder
Open Pipes are pipes that have open ends and flute mouths, (like a recorder)