A reference period is the time period for which statistical results are collected or calculated and to which, as a result, these values refer. The time period may be either a calendar year (reference year), a fiscal year, a semester, a quarter, a month and even a day.

Some data, like population variables, relate to one specific time, a reference time point (e.g. a specific day, population on the 1st of January).

The reference period should be distinguished from the publication time, the period or point in time at which the statistical data are published. The publication year of statistical results may be significantly later than the reference year for which they were collected.

Source: EUROSTAT

The collected information shall refer to a single reference year that is common to all Member States by referring to the situation during a specified timeframe or date as follows:
(a) For land variables, the use of the land shall refer to the reference year. In the case of successive crops from the same piece of land, the land use shall refer to a crop that is harvested during the reference year, regardless of when the crop in question is sown.
(b) For variables on irrigation and soil management practices, the reference period is a 12-month period ending within the reference year, to be established by each Member State with a view to covering the related production cycles.
(c) For variables on livestock, animal housing and manure management a common reference day within the reference year shall be established by each Member State. The variables on manure management shall refer to a 12-month period including that date.
(d) For variables on labour force, a 12-month reference period ending on a reference day within the reference year shall be established by each Member State.
(e) For variables on rural development measures implemented in the individual agricultural holdings, the reference period shall be the three-year period ending on 31 December of the reference year.
(f) For all other variables, a common reference day within the reference year shall be established by each Member State.

Source: EURO-Lex

The reference CO2 emissions shall be based on the monitoring data reported pursuant to Regulation (EU) 2018/956 for the period from 1 July 2019 to 30 June 2020 (‘the reference period’), excluding vocational vehicles, and shall be calculated in accordance with point 3 of Annex I to this Regulation.

Source: EURO-Lex

The reference period for the EAA is the calendar year.

Source: EURO-Lex

(Risk) Expected losses (of lives, persons injured, property damaged and economic activity disrupted) due to a particular hazard for a given area and reference period. Based on mathematical calculations, risk is the product of hazard and vulnerability.

Source: EEA Glossary