HASL or HAL (for hot air (solder) leveling) is a type of finish used on printed circuit boards (PCBs).
The PCB is typically dipped into a bath of molten solder so that all exposed copper surfaces are covered by solder.
Excess solder is removed by passing the PCB between hot air knives.
[1] HASL can be applied with or without lead (Pb), but only lead-free HASL is RoHS compliant.