Quant indicates a specific stock quantity of the same product that entered your warehouse at a specific moment in time in one specific operation; in a single lot (batch) if lot tracking is enabled.
Let's give an example. You purchased 10 pieces a week ago, you received 6 pieces yesterday and today the remaining 4 pieces arrive. In this case, two quants will be created: 1 with 6 pieces, another one with 4 pieces. Should the batch with 4 pieces be linked to individual Lot (serial) numbers, the result will be 4 separate quants.
The Quants table stores the current state of stock (per location). It is updated each time a stock move is set to done and has 3 main impacts:
A quant optimizes the computation (e.g. quantity available), because a quant only contains information about the current stock (not the past or the future). The volume is smaller and doesn’t grow in time;
A quant will be used in FIFO, LIFO and FEFO costing, as we need to match the incoming and outgoing moves for a correct stock valuation;
A quant can also be used for upstream/downstream traceability and lot management; a quant contains the information about lots. Quant history displays a list of stock moves indicating the current stock level.
In case a quant has been reserved, you can see the related stock move in the Reserved for Move field. Quants can be split in order to reserve only the quantities needed.