Definition of retention time on the web is as below
The time it takes for the volume of water in a lake to exit through its outlet (ie, total volume/outlet flow = retention time).
www.epa.gov/glnpo/rptcong/1994/glossary.htmt: The time taken by the analyte peak to reach the detector after sample introduction is called the retention time. A more accurate measure of the retention time of an analyte is obtained by subtracting from this value the time taken for an unretained solute to emerge from the column (ie, the dead time, t 0 ), resulting in the adjusted retention time, t’. The retention time is the most important parameter for component identification under set experimental conditions.
www.laballiance.com/la_info/support/hplc2.htmtime, usually in days, required for a volume of water equal to the reservoir capacity to move through the reservoir and be discharged downstream.
www.ncwater.org/About_DWR/Water_Projects_Section/Instream_Flow/glossary2.htmis the amount of time in which a given set of data will remain available for restore. Some backup products rely on daily copies of data and measure retention in terms of days. Others retain a number of copies of data changes regardless of the amount of time.
en.wikipedia.org/wiki/BackupsThe length of time required for a compound of component of a mixture to pass through a chromatographic column.
www.fire.org.uk/glossary.htm