High- and low-level

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.
Features which emerge only at a high level of description are known as epiphenomena.
Differences.
Due to the nature of complex systems, the high-level description will often be completely different from the low-level one; and, therefore, the (different) descriptions that each deliver are consequent upon the level at which each (differently) direct their study. For example,