From Science Europe Data Glossary
Definition: a data set (or dataset) is any organized collection of data.
Explanation: the terms database and data set are sometimes used interchangeably, although a database is actually a type of a data set. A research data set should meet the requirements of being assessable, discoverable, intelligible, interoperable to specific quality standards, and useable beyond the original purpose for which it was collected.
References: http://stats.oecd.org/glossary/detail.asp?ID=542; http://ec.europa.eu/research/participants/data/ref/h2020/grants_manual/hi/oa_pilot/h2020-hi-oa-data-mgt_en.pdf
See also: FAIR data; data sharing