0 a theory that says that the most basic pieces of matter are extremely small lines or circles rather than points
1 a theory explaining the character of matter and the forces of the universe, based on the idea that they behave more like closed circles of string than like points
String theory is of course, not a proven theory.
The anthropic landscape of string theory, hep-th/ 0302219.
We note that this is compatible with string theory, in the sense that there are a great many string vacua, which likely populate the space of low energy parameters well.
These calculations are then used to determine the probabilities of various physical processes in string theory.
In string theory, a string may be open (forming a segment with two endpoints) or closed (forming a closed loop).
D-branes are dynamical extended objects of various dimensionalities predicted by string theory that could play this role.
The full physics of string theory can always be thought of as a system of infinitely many quantum fields expanded around a given string background.
Recent developments in string theory suggest that the string theory landscape of vacua is vast.
