What does chmod 654 stand for?

in my computer i am using linux. and one day i saw chmod 654 message written some where so Can anyone explain me what is chmod 654 stands for and what is the use of it in computer?

Chmod is nothing but a Linux command which is used to change permission mode. The full form of chmod is change mode. And 654 is it’s binary equivalent.

Command to change permission mode (chmod) appears with chmod rwx.654. Whereas rwx means: read, write, execute. And 654 is its binary equivalent but the first number represent the owner that is 6, second number represent group and third number represents everyone.

Each character of rwx represents its own value. Whereas r is read, w is write and x is execute. This combines and makes various combinations such as:
rwx-r-x which mean the owner is allowed to read, write and execute and group is only allowed to read and everyone are allowed to execute.
This binary equivalent values never produce ambiguous combination each sum represent a specific set of permission
Here is the individual meaning of the octal digital value:
0 - - - (no permission to do anything)
1 - - x (execute)
2 – w- (write)
3 – w x (write and execute)
4 r - - (read)
5 r – x (read and execute)
6 rw- - (read and write)
7 rwx - - (read, write and execute)

And this is the binary counting:
0: 000
1: 001
2: 010
3: 011
4: 100
5: 101
6: 110
7: 111

If you will change permission mode to chmod rwr. 654 it will mean: the user can read and write and group can read and execute but cannot write and everyone can read only what ever the data is.