When viewing or creating a script, the very first line of the script will be the interpreter the script should use. In this example, the BASH interpreter is being used.
The interpreter tells Linux what language the script was written in so that the appropriate interpreter can be used when running the script. Imagine the script interpreter like a translator. You've a bunch of people speaking different languages (English, Mandarin, Spanish, Russian). Fortunately, the interpreter is really smart and understands each language.
Technically speaking, the #! characters are the shebang.
Following are some popular script interpreters.
Each script interpreter has its own unique syntax.