A minimum order quantity (MOQ) is the minimum order size accepted by a supplier. Generally, this is based on the minimum order the supplier needs in order for the transaction to be profitable for them. Sometimes they may accept smaller orders for a higher price per unit. With most suppliers, the more you order, the greater your discount.
While some suppliers do not enforce minimum orders, they are essential for many wholesalers who rely on large orders to make a profit. Most wholesalers only make small margins on each item they sell. Sometimes this means that small orders can cost them a lot of time and effort to process, and there is little financial gain, hence why larger orders are more profitable.