According to Wikipedia, the low level languages are machine code and assembly.
From the source:
In computer science, a low-level
programming language is a programming
language that provides little or no
abstraction from a computer's
instruction set architecture. The word
"low" refers to the small or
nonexistent amount of abstraction
between the language and machine
language; because of this, low-level
languages are sometimes described as
being "close to the hardware."
Then, to answer:
So why does everybody keep mentioning high and low-level languages if assembler is really the only low-level language.
I don't know who "everyone" is, but I would venture a guess that back when high-level languages were not as commonplace as they are today, it was more relevant to talk about low-level vs. high-level (because there was a relatively significant amount of programmers writing assembly code). In modern times it is a less important distinction. Personally, I rarely hear people using these terms except to differentiate between assembly or not (except for those times when you might hear someone raised on Python referring to C or C++ as low-level, but this is not in the spirit of the original definition).