How can you define such terms as overgrazing and taxonomy?

Overgrazing is the intensive animal consumption of plants, which extracts an unsustainable yield of floral biomass from an ecosystem, typically over an extended period and without a sufficient recovery period. Overgrazing is most commonly caused by a high density of animals such as cattle, sheep, and goats on an area of land with the lack of rotation to other areas and grazing at an inappropriate time in the relation of the land to recover. Overgrazing also causes soil erosion, reduces the usefulness, productivity and biodiversity of the land and may lead to soil compaction, reduction in long-term grazing productivity, loss of topsoil, and increases in surface runoff and flooding.

Taxonomy is the organization of life into a hierarchy of groups of increasingly closely related species. This system is called taxonomic classification. The broadest classifications are by domain and kingdom; the most specific classification is by genus and species. The hierarchical groupings in between include phylum, class, family, orders, genera and species. Within each taxonomic group, there are several species which are known as model organisms, they are the best-studied species within a taxonomic group allowing scientists to make comparisons to them with other species which are difficult to find out more about.

First life is split into domain classifications which are called Archaea, Bacteria, and Eukaryota.

Archaea are single-celled and differ from other forms of life in their ribosomal RNA structure and in the molecular structure of their lipids. There are around 4000 different types which are only known from genomic sequences sampled from the environment. There are no known parasitic or pathogenic members of this domain.