Open Data generally refers to machine readable data which is made freely available (or available under licence) for public consumption. If your question is not closely related to programming, please consider to ask your question on https://opendata.stackexchange.com.
Open Data refers to data which has been made available for public consumption. In general open data is made available by governments or government controlled agencies, often referred to as Open Government Data (OGD), but in reality it can refer to any data made available by any agency, be they a corporate or government entity.
Definitions of Open Data in Literature
[1] Machine readable data made available by governments or government controlled agencies under open licence conditions that allow for further commercial or non commercial use of the data (Janssen and Darbishire, 2012).
[2] Data and information produced or commissioned by the government or government controlled agencies (Lee, 2012, p.1).
Open Data Formats
Open Data can be made available in any formats, but the most popular formats include: CSV, XML, XLS, XLSX, JSON, RDF, RSS, PDF.
Example Open Data Repositories
References
[1] Janssen, K and Darbishire, H (2012) Using open data: is it really empowering? In: W3C (World Wide Web Consortium), Using Open Data: policy modeling, citizen empowerment, data journalism. Brussels, Belgium 19-20 June 2012.
[2] Lee, D (2012) Open Data Overview [Online]. Available: http://www.iia.ie/resources/download/581/ [Accessed 19 May 2012]
