- Animal aggregation: A concentration of animals (rare species, common species, or a mixture of the two) that occurs during a species' life cycle. Animals in these aggregations are highly vulnerable to disturbance. Examples are colonial waterbird nesting sites, bat hibernacula, and mussel beds.
- Ecological classification system (ECS): A system for identifying, describing, and mapping progressively smaller areas of land with increasingly uniform ecological features. Ecological classification systems are developed by integrating climatic, geologic, hydrologic, topographic, soil, and vegetation data. They aid in ecologically guided management of natural resources at different scales across the landscape. Minnesota's ECS describes land in six levels of increasing detail: provinces, sections, subsections, land type associations, land types, and land type phases.
- Endangered species: A plant or animal species that is threatened with extinction throughout all or a significant portion of its range in Minnesota.
- Native plant community: A group of native plants that interact with each other and the surrounding environment in ways not greatly altered by humans or by introduced plant or animal species. These groups of native plants form recognizable units, such as an oak forest, a prairie, or a marsh, that tend to repeat across the landscape and over time. The classification of native plant communities currently used by the Minnesota County Biological Survey was developed from analysis of thousands of plot samples recorded in native plant communities across Minnesota.
- Rare species: A plant or animal species that is designated as endangered, threatened, or a species of special concern by the state of Minnesota (this includes all species designated as endangered or threatened at the federal level), or an uncommon species that does not—or does not yet—have an official designation, but whose distribution and abundance need to be better understood.
- Sites: Areas of land, ranging from tens to thousands of acres in size, selected for survey by MCBS because they are likely to contain relatively undisturbed native plant communities, large populations and/or concentrations of rare species, and/or critical animal habitat. Sites provide a geographic framework for recording and storing data and compiling descriptive summaries.
- Special Concern species: A plant or animal species that is extremely uncommon in Minnesota, or has a unique or highly specific habitat requirements and deserves careful monitoring. Species on the periphery of their ranges may be included in this category, as well as species that were once threatened or endangered but now have increasing, or stable and protected, populations.
- Threatened species: A plant or animal species that is likely to become endangered within the foreseeable future throughout all or a significant portion of its range in Minnesota.