Answer:
The most basic difference is that the statements in a low level language can be directly mapped to processor instructions, while a single statement in a high level language may execute dozens of instructions.
Low level refers to the fact that this is a machine language, binary in form, generally meaning one low level command = one executed instruction.
The complexity arises when we need to enable a programmer to designate one high level instruction that performs several or many machine (low level) operations.
Low Level Languages: Assembler and Advanced Assembler - see Compiler Languages.
High Level Languages: RPG, COBOL, any that make machine level programming of a computer easier.