Gathering interface 1/9999 on shards?

[Pintsized]

It means that the items 'stack' into a single inventory/bank slot, to the maximum number shown in the /nnn, rather than needing a slot for each individual item of that type. Shards used to be stacked at far lower numbers but the stack size got increased due to the large number of shards crafters use in short periods of time.

The 'stack' number is also the maximum number of that item that you can sell in a single Auction House sale.

When you drag a stack, from say your inventory to your bank, a pop-up will allow you to 'split the stack' into two smaller stacks of a size you can select.