The -z option is used to list readable strings found in the .rodata section of ELF binaries, or the .text section of PE files. Example:
$ rabin2 -z /bin/ls | head
000 0x000160f8 0x000160f8 11 12 (.rodata) ascii dev_ino_pop
001 0x00016188 0x00016188 10 11 (.rodata) ascii sort_files
002 0x00016193 0x00016193 6 7 (.rodata) ascii posix-
003 0x0001619a 0x0001619a 4 5 (.rodata) ascii main
004 0x00016250 0x00016250 10 11 (.rodata) ascii ?pcdb-lswd
005 0x00016260 0x00016260 65 66 (.rodata) ascii # Configuration file for dircolors, a utility to help you set the
006 0x000162a2 0x000162a2 72 73 (.rodata) ascii # LS_COLORS environment variable used by GNU ls with the --color option.
007 0x000162eb 0x000162eb 56 57 (.rodata) ascii # Copyright (C) 1996-2018 Free Software Foundation, Inc.
008 0x00016324 0x00016324 70 71 (.rodata) ascii # Copying and distribution of this file, with or without modification,
009 0x0001636b 0x0001636b 76 77 (.rodata) ascii # are permitted provided the copyright notice and this notice are preserved.
With the -zr option, this information is represented as a radare2 commands list. It can be used in a radare2 session to automatically create a flag space called "strings" pre-populated with flags for all strings found by rabin2. Furthermore, this script will mark corresponding byte ranges as strings instead of code.
