What is robots.txt?

[aliceta]

The robots exclusion standard, also known as the robots exclusion protocol or simply robots.txt, is a standard used by websites to communicate with web crawlers and other web robots. The standard specifies how to inform the web robot about which areas of the website should not be processed or scanned.

[Techila]

According to my opinion it is one of the text file which will instruct the google for indexing and fetching.