CHMOD is short for change mode, a UNIX command that changes the access permissions of files or directories in order to read, write or execute files.
ASCII mode - American Standard Code for Information Interchange, 256 character mode, numbered from 0 to 255. Letters begin at 65 (A) and 97(a), numbers are mid-40s and punctuation mostly before that. (aka, ANSI - American National Standards Institute)
Binary (0s and 1s) mode - mode of 256 characters from 0000000 (0,0+0+0+0+0+0+0+0) to 1111111 (255, 1+2+4+8+16+32+64+128)
Here is the ASCII table, printable characters are shown at the far right (off screen on 1024 width monitor): ASCII (ANSI) Table