High-level and low-level, as technical terms, are used to classify, describe and point to specific goals of a systematic operation; and are applied in a wide range of contexts, such as, for instance, in domains as widely varied as computer science and business administration.
High-level describe those operations that are more abstract in nature; wherein the overall goals and systemic features are typically more concerned with the wider, macro system as a whole.
Low-level describes more specific individual components of a systematic operation, focusing on the details of rudimentary micro functions rather than macro, complex processes. Low-level classification is typically more concerned with individual components within the system and how they operate.
In Computer Science, software is typically divided into two types: high-level end-user applications software (such as word processors, databases, video games, etc.), and low-level systems software (such as operation systems, hardware drivers, etc.).
As such, high-level applications typically rely on low-level applications to function.
In terms of programming, a high-level programming language is one which has a relatively high level of abstraction and manipulates conceptual functions in a structured manner.
A low-level programming language is one like assembly language that contains rudimentary microprocessor commands.