Discrete is used for single order picks, bulk and batch are for multiple order picks.

Discrete picking is typically one order, system-like picking that does not include mechanisms to shorten picking or travel time.

In bulk picking, the orders that can be collected to form a bulk pick are sales, distribution, and works orders. These bulk picks accumulate the items together, and, using the defined picking rules, issue the instructions to the staff to pick the stock. The total item quantity is picked and sorted to individual orders during a subsequent step.

Batch picking lets warehouse staff pick items in a more efficient way. Batch picking reorders the order-picking sequence and tasks so warehouse staff can pick multiple items from multiple orders at various locations throughout the warehouse with a shortened travel sequence. The items are sorted to the individual orders during the pick process.

As a general rule, smaller warehouses use discrete order picking while higher volume (based on number of order picked) warehouses take advantage of batch picking. Bulk picking is used to a lesser degree.