Z2E
Z2E stands for Zelda 2 Enhanced (video game)
Z3
Z3 stands for Zero 3 (Street Fighter: Zero 3 game)
Z4Z
Z4Z stands for Z for Zachariah (science fiction)
Z4K
Z4K stands for Zombies for Kevin
Z64
Z64 stands for Zelda 64 (game)
z/OS
z/OS stands for Z Series Operating System (IBM mainframe operating system)
Z-LCF-L
Z-LCF-L stands for Creep Strength and Low-Cycle Fatigue Test Loop (material production)
Z80
Z80 stands for Zilog Z80 8-bit microprocessor chip
z/w
z/w stands for Zaraz Wracam (Polish: Be Right Back)
Z-Hour
Z-Hour stands for Hour Set for Attack (US Navy)