categories of red data book – these categories, applied to all the species included in the Red Data Book express the extent, to which the given species is endangered.

endangered species – the species threatened with total extinction or vanishing from a certain region. The numbers of the endangered species are either critically low or their distribution area has shrinked or is about to decrease to an extremely small size. The species can equally considered to be endangered if their habitats have been destroyed or damaged. Species extinct in certain area or worldwide are usually also included to the endangered species list.

IUCN - The World Conservation Union is a worldwide partnership of states, government agencies and NGOs. Its mission is to influence, encourage and assist societies throughout the world to conserve the integrity and diversity of nature and to ensure that any use of natural resources is equitable and ecologically sustainable. The IUCN Red Data List is the world's most comprehensive inventory of the global conservation status of plants and animals.

red data book – published red data list. These terms are often used as synonyms.

red data list – the list of endangered species and intraspecific taxa (subspecies, varieties, forms and sometimes also populations). Occasionally the data about distribution, ecology, protection needs etc. are added (see also red data book).

taxon – any formal unit or category in a biological classification. In a Red Data Book the term “taxon” is mainly used for species and intraspecific units like subspecies, varieties and forms.