Define red data book.

Hint: The IUCN Red List provides a systematic list of plants and animals in different categories. It uses a series of standards to assess the risk of extinction of thousands of species and subspecies.

Complete Answer:
- The Red Data Book is a reference book that holds a list of all endangered animals and plants. There are various Red Data Books for plants, animals and other species.

- The IUCN Red List is generally regarded as the most systematic and objective global guide to determining the survival status of various plant and animal species. It includes information on the environment, population size, biodiversity and ecosystem, usage, risks and management activities that can help inform the required conservation decisions. The IUCN Red List is used by various agencies such as government agencies, wildlife departments, NGOs involved in conservation, educational organisations, students, business community, etc.

- The IUCN Red List is based on clear guidelines for evaluating the likelihood of extinction of thousands of species and subspecies. These criteria are applicable to all animals and to all regions of the planet. The goal is to express the importance of environmental concerns to the public and decision makers, as well as to help the international community to try to mitigate species extinction. IUCN has categorised animals into groups of Extinct, Extinct in the wild, Vulnerable, Endangered, Critically Endangered, etc. based on data gathered worldwide.

Note: The IUCN Red List is important not only to help recognise certain species that require focused rehabilitation efforts, but also to focus the conservation agenda by recognizing key locations and environments that need to be protected.