Assembly.

A programming language. Totally low-level language like the machine code.

Since machine codes totally suck at reading to the human eye, it was developed to make it
at least readable. The commands and the machine code are matched 1:1.
However, since machine codes are unique to their CPUs, assembly itself is also unique to it's owner. To be precise, the language differs to it's architecture.

For example, a machine code

001000 00001 00000 0000000000001010

the assembly equivalent to that code

addi $1, $0, 10

well, it is kinda a little better to read.
One with a good imagination can at least guess what the hell the example sentence meant.
(yeah, people call that a benefits to assembly.)

Since the language is only good at reading out loud, one will have to memorize the computer's WHOLE FREAKING CPU structure. Because of that reason assembly lost to the "fresh and new" high-level languages(C, C++, JAVA, stuff like that) in modern programming.

However, when handling system drivers and embeded stuff, these babies are still up and high.
And assembly is used to optimize high performance programs (everyday games, or CAD or hard core graphics stuff)