The Open Knowledge Foundation defines open data as “data that can be freely used, shared and built-on by anyone, anywhere, for any purpose.” Another definition is that open data are online, free of cost, accessible data that can be used, reused and distributed provided that the data source is attributed.
Formats of Data
Open data include data combined in the form of datasets, text files (csv) and spreadsheets but also include non-textual material such as visualizations, maps, genomes, chemical compounds, mathematical and scientific formulae, and medical data among others.
The 2 areas of Openness for data
Openness encompasses 2 areas -- legal openness (allowing others to get the data legally, to build on it, and to share it) and technological openness (removing technical barriers to access and using data).
How does Open Data relate to other open methodologies
Open Data is a significant element of Open Science which refers to the process of conducting science within a collaborative environment and with a focus on research communication. Open science (and therefore Open Data) comprises both principles (transparency, reuse, participation, accountability, etc.) and practices (open publications, data-sharing, citizen science, etc.). Open scholarship is a broader term encompassing Open Science.
The goals of open data are similar to those of other "open(-source)" movements such as open-source software, hardware, open content, open education, open educational resources, open government, open knowledge, open access, and the open web.
The Foster Heirarchy demonstrates the concentration areas in Open Data as they relate to other Open Science initiatives.