3PL: A third-party logistics provider: a warehouse that stores, picks, packs, ships and often processes returns on behalf of several merchant clients.
Merchant (client): A brand or retailer whose goods a 3PL handles. In returns processing, each merchant has its own grading rules, dispositions and service level.
Return-to-stock time: The hands-on time per unit from the scan that opens it at the bench to the put-away that closes it. Measured per unit, averaged over a period.
RMA: Return merchandise authorisation. The record a merchant or portal creates when a shopper starts a return, usually carrying a number, a label and a reason.
Return portal: The shopper-facing site where a return is started: order lookup, item selection, reason, and a label. Some portals belong to the merchant, some to a 3PL.
SOP: Standard operating procedure. In returns, the merchant's rules for inspecting their goods: which issues to look for, when to photograph, and what each issue should become.
Issue: A defect or condition found on inspection, such as worn, stained, missing tags or damaged in transit. Issues are the inputs the disposition is decided from.
Grading: Inspecting a returned unit and recording its issues and condition against the merchant's rules. The output is a grade and a recommended disposition.
Photo evidence: A photograph taken at the bench and stored against a specific issue on a specific unit, so a later dispute about condition can be settled from the record.
Disposition: What happens to a unit after grading: return to stock, dispose, donate, return to merchant, hold, quarantine, or missing item.
Restock: Returning a unit to sellable inventory, including the write-back to the system that holds stock levels.
Restock SKU: The SKU a graded unit is restocked under when it differs from the one it was sold as, for example an open-box or B-grade variant.
Value-added service (VAS): Work done to a returned unit beyond inspection: repair, cleaning, repackaging, re-tagging. Each has an outcome and, at most 3PLs, a price the merchant is billed.
License plate (LPN): A printed barcode attached to a unit that leaves the bench for a longer service, so it can be tracked while out and scanned back in to resume its return.
Put-away: Moving a unit from the bench to its storage location and recording the bin it went into.
Bin location: The named shelf position a SKU is stored in, such as A-12-03. The last known bin for a SKU is what a put-away screen prefills.
SLA: Service level agreement. For returns, the window a 3PL commits to for processing a merchant's return after it is received, usually 24 or 48 hours.
Blind return: A unit that arrives with no RMA or advance notice. It has to be identified and recorded from the parcel and the item itself before it can be processed.
Label template: The layout a 3PL prints for a merchant's product or packet labels, with a barcode format such as Code 128, QR, EAN-13 or UPC-A.
Hands-on time: The time a processor is actively working on a unit, as opposed to the time the unit spends waiting. Return-to-stock time is hands-on time per unit.

The one term worth a whole page is return-to-stock time. The Return to stock time page covers the formula, how to measure it in any system, and what moves it.