The MacPherson strut suspension is the most compact and lightweight independent suspension available. While it still has many of the disadvantages of other suspension systems, its space and weight savings, coupled with low cost, make it a very popular suspension for automobiles, especially in the front. It can be used for driven or non-driven wheels. In small automobiles, the front is typically a MacPherson system, and the rear is torsion bar, multilink, or double wishbone.
Invented in the 1940s by Earl S. MacPherson of Ford, and introduced on the 1950 English Ford, this is now one of the most prevalent types of suspension. While typically used only in front suspension designs, some vehicles like the Lancia Delta of past WRC fame used it at all four corners. It is especially useful in the front because the engine takes up a certain non-negotiable amount of space. Using a MacPherson system rather than a double wishbone, fixed axle, or multilink design saves you quite a bit of room.
In brief, the difference between a shock and a strut is that a shock has pivoting links on both ends, and a strut is fixed at one end. On a MacPherson strut suspension, the bottom end of the strut is fixed to the suspension upright, and the top is attached to a strut tower by a pivoting attachment point. There is a single A-Arm at the bottom of the upright, which attaches to the frame of the car.
The disadvantage of a MacPherson suspension is that camber is not constant. You can however adjust the camber, and even the caster by installing an upper mount (at the top of the shock tower) which can be adjusted by sliding the upper mount of the strut. This is not typically possible with stock components, but you can add an aftermarket adjustment kit to perform this function. Depending on whether they alter only camber, or caster as well, they are known either as "camber plates" or "camber/caster plates", sometimes with the word "adjustment" thrown into the middle. Generally speaking you will also need to replace the lower control arm with an adjustable-length link for full adjustment.