In the following context I would like to know what a binary file means.
The mode argument of the fopen() function can also take value b to indicate that the openend file should be treated as a binary file.
Another excerpt from the same text block:
The default mode of fopen() function has been set to binary for all platforms that distinguishes between text and binary file.
A binary file is a possibly non-text file such as images, videos or zips... anything could be read as a binary. Compiled code is another example of this.
A binary file is anything a Computer could interpret and you by just reading it cannot.
Note: You could cast a text file as a binary too, if you want.