From Just Solve the File Format Problem
A shebang (also called a hashbang, and other equally silly names) is line of text that associates a file (usually a script to be interpreted) with an application. The technique is crude but effective, and is ubiquitous on Unix-like systems.
If one attempts to execute a file whose contents begin with "
#!", a Unix-like operating system looks for the name of a program after the "#!", and executes that program instead, with the original file as a parameter. This effectively makes the original file itself executable.
An example of a shebang is