This document defines and provides examples of open data, open government data, open policy, open science, and open linked data. It explains that open data is data that can be freely used, reused and redistributed subject to attribution and share-alike requirements. Open government data allows citizens to participate in government decisions. Examples of open data portals for different governments are provided. The document also discusses how open data, including research data, can be shared and used under open licenses to advance science and education.