$f0–$f31 registers: The 32 general-purpose 32-bit floating-point registers. In MIPS I (32-bit) CPUs, only even-numbered registers can be used for arithmetic (the odd-numbered registers hold the low-order bits of 64-bit, double-precision numbers).
$n register: One of the CPU’s 32 general-purpose registers.
a0–a3 register: Aliases for CPU registers $4–$7, conventionally used for passing the first four words of the arguments to a function.
ABI (application binary interface): A particular standard for building program binaries that in turn is supposed to guarantee correct execution on a conforming environment. MIPS32 CPUs generally use a standard known as o32, while for 64-bit operation there’s a choice of n32 and n64. Many embedded ...