Internal RAM, or IRAM, is the address range of RAM that is internal to the CPU. Some object files contain an .iram section.
Generally, IRAM is composed of very high speed SRAM located alongside of the CPU. It acts similar to a CPU cache, but is software addressable. This saves transistors and power, and is potentially much faster, but forces programmers to specifically allocate it in order to benefit. In contrast, cache is invisible to the programmer.
Application
The Rockbox project makes use of IRAM to improve the performance of its codecs. The Rockbox developers have expanded their binaries by two segments: .iram and .ibss, roughly similar to .data and .bss, though, affected variables are stored in the IRAM memory area.
References
Internal RAM Wikipedia(Text) CC BY-SA