I'm writing about the trusses made of
wood and
metal. These are the major structural components of
roofs and
floors. Most roof trusses are made with only 2x4
boards but many make use of 2x6's.
Trusses made for roofs are generally shaped like an isosceles triangle (something like this /_\ only imagine the two side lines to up to meet at a peak and the bottom line to meet the corners).
Commons
Trusses with this shape are called "commons". The two boards of equal length running up the side are called "top chords" and the bottom board is called the "bottom chord". The place at which the two top chords meet is the "peak". The place at which a top chord meets a bottom chord is called the "heel".
Plates
Of course, the boards involved must be attached somehow to one another. They are attached with are as "plates". A plate is basically a metal plate with sharp metal teeth attached to it. Plates come in various sizes as different coverage is needed for different joints on the truss. A given plate is referred to by its size; length by width. So, you'd say, "Yo, Tony, me a five by five for this peak!". Modern plates are coated with an oil to prevent rusting. The teeth on modern plates are arranged in a wave pattern to increase the "grip" a plate can get.
Webs
You'll rarely see a truss with only top chords and bottom chords. Most of the time, other boards are used to increase stability and better distribute weight and tension. These are called "webs". The most common web is the "king post" runs up the middle of the truss, from bottom chord to peak. Very few trusses are manufactured without a post. Other webs may extend from the bottom of the king post to the middle of the top chord on each side. These are called "side webs". Some webs stand upright like the king post but do reach the peak. These are called "uprights". The webs closest to the heel of the truss are called the "end webs".
Trusses made of steel are increasingly common in construction, though their presence is more widely felt in industrial framing than in residential. Steel trusses far stronger than wood trusses but require much more skilled labor in their production and installation as is much welding involved.