BIPM : Bureau Internationnal des Poids et Mesures ; this is BIPM time department that is in charge of the calculation of the international time references (EAL, TAI, UTC, UTCr, the SI second)
 EAL : Echelle Atomique Libre ; it is the first step of the calculation of UTC. This is performed at the end of each month using the clock data collected during the previous month. This step consists in computing a weighted average of the commercial clock data transmitted to the BIPM (about 400 clocks worldwide)
 TAI: Temps Atomique International ; it stems from the frequency steering of EAL using primary frequency standards calibrations, provided by about half a dozen cold atom fountains. The SYRTE fountains have contributed to about 40% of this steering over the past decade.
 the SI second: it corresponds to a weighted average of the primary frequency standard calibrations transmitted to the BIPM at the end of the month.
 UTC: Temps Universel Coordonné; it is equal to TAI modulo 1s. UTC is maintained close to UT1, the timescale based on Earth rotation observations calculated by IERS by inserting leap seconds. A leap second is inserted if the departure between UTC and UT1 is larger than 0.9 s.
 UTC(k): the local real time representation of UTC realized by laboratory k ; there is usually one main laboratory designated to generate the national realization of UTC per country
 UTC(OP) : Temps Universel Coordonné generated at Observatoire de Paris ; It is the French realization of UTC, at the basis of legal time in France
 legal time : in France, it is equal to UTC (OP) + 1 hour in winter and UTC (OP) + 2 hours in summer