Mb-a unit of information equal to 1000 kilobits or 10^6 (1,000,000) bits. Mbit, megabit. computer memory unit-a unit for measuring computer memory. kb, kbit, kilobit-a unit of information equal to 1000 bits. Gbit, gigabit, Gb-a unit of information equal to 1000 megabits or 10^9 (1,000,000,000) bits.