IFR fuel planning (reserves)

Trip fuel: fuel from start of taxi to landing at the destination.
Contingency fuel: covers deviations from the planned operation (e.g. wind, routing changes).
Alternate fuel: fuel to fly a missed approach at the destination, climb, route to, and approach/land at the alternate (when one is required).
Final reserve fuel: fuel for a specified holding time at 1500 ft above the alternate (or destination) elevation in standard conditions — 20 minutes for helicopters under EASA rules (aeroplanes use 30 minutes).
Additional/extra fuel: any further fuel the commander judges necessary (isolated aerodrome, extended holding, etc.).
Declare "MINIMUM FUEL" to ATC if usable fuel is expected to be less than final reserve on landing; declare a fuel emergency ("MAYDAY MAYDAY MAYDAY FUEL") if it will be, or already is, below final reserve.

Source: EASA Air Ops – CAT.OP.MPA.150 / NCC.OP – Fuel policy