M-theory is an unification and extension of string theory. String theory requires 6 dimensions beyond the 4 (3 space, 1 time) that we are already familiar with for a total 10 dimensions. Further more as string theory developed 5 different versions were produced. M-theory resulted from the simple addition of an 11th dimension, resulting in a unification of 5 different versions of String theory.
The result is a unification of the four forces of nature including gravity in a single theory. This accomplishment has one down side and that is the difficulty of finding evidence of these higher dimensions. It does however make predictions that should be testable is the world’s larges super collider. The powerful particle accelerator can produce the energy levels need to look into the small scales where there these extra dimensions can be detected. However this super collider has so far failed to find the evidence predicted by m-theory
It was discovered that by adding this 11th dimension that a string could be stretched out to form a membrane or brane for short. Furthermore strings could be attached to a bane forming the bases for a universe. It provides the vary fabric for space-time general relativity showed exists.
M-theory is a theoretical concept that has much potential. It expands our view of reality beyond which science has previously considered. It opens up new possibilities science would previous been closed to.