Primary data is the type of data that is collected by researchers directly from main sources while secondary data is the data that has already been collected through primary sources and made readily available for researchers to use for their own research.

For example, a photograph or video of an event is a primary source. Data from an experiment is a primary source. Secondary sources are one step removed from that. Tertiary sources summarize or synthesize the research in secondary sources. For example, textbooks and reference books are tertiary sources.

Tertiary sources are sources that identify and locate primary and secondary sources. These can include bibliographies, indexes, abstracts, encyclopedias, and other reference resources; available in multiple formats, i.e. some are online, others only in print.

Examples of Tertiary Sources: Dictionaries/encyclopedias (may also be secondary), almanacs, fact books, Wikipedia, bibliographies (may also be secondary), directories, guidebooks, manuals, handbooks, and textbooks (may be secondary), indexing and abstracting sources.

Tertiary sources are publications that summarize and digest the information in primary and secondary sources to provide background on a topic, idea, or event. Encyclopedias and biographical dictionaries are good examples of tertiary sources.

Examples of secondary sources include:

• journal articles that comment on or analyse research.
• textbooks.
• dictionaries and encyclopaedias.
• books that interpret, analyse.
• political commentary.
• biographies.
• dissertations.
• newspaper editorial/opinion pieces.

A tertiary color or intermediate color is a color made by mixing full saturation of one primary color with half saturation of another primary color and none of a third primary color, in a given color space such as RGB, CMYK (more modern) or RYB (traditional).