IMPREST An Imprest account is a stock location that is replenished to an agreed stock level on a regular basis, without requiring a purchase order. It can also be a remote location (satellite facilty) or a customer that you have lent stock or eqipment to. Stock are usually 'transferred' to the imprest location then recorded as being consumed by a point-of-sale allocation.
UNBILLED Relating to Cost Centres, when stock items are allocated to a Cost Centre the period is still open and is able to have more items added to it. An item becomes BILLED when it has been included within a Closed-Off period. All Billed items are cleared from the Cost Centre edit grid (Office > Cost Centres)