it means Selamat Hari Raya Maaf Zahir Batin, short form for Eid Fitr, and sorta apologizing for everything that you have done. they are Malay words. usually they are written for simplicity (obviously because it is shorter), saying it out loud would be weird though
Farah : hey Mira, SHRMZB!
Mira : thanks, you too, SHRMZB