The number of bits that can be stored within a given physical area. See bpi.
A Memory Bit
This is one storage cell in an earlier 16-megabit DRAM memory chip. Although minuscule in overall capacity compared to today's memory, there were 16,777,216 of these cells in the chip, which was only a quarter of an inch square. (Image courtesy of International Business Machines Corporation. Unauthorized use not permitted.)