Sell-in vs sell-through: the basic definition
Sell-in is the wholesale transaction: your brand ships N units to the retailer and invoices them. Revenue is recognized. Sell-through is the retail transaction: the end consumer buys one of those N units and walks out of the store with it.
A brand with great sell-in can still be in trouble. If the retailer bought a full pallet and sells only 15% of it, they are going to mark it down, return it, or cancel the next PO. Sell-through is the leading indicator; sell-in is the lagging one.
Why the distinction matters
Finance teams typically report on sell-in because that's where revenue recognition happens. Sales and trade marketing teams live and die by sell-through because that's what determines the next PO, shelf space, and category status inside the retailer.
Brands that thrive in wholesale treat sell-through as the primary KPI and sell-in as a downstream result. Brands that collapse in wholesale do the opposite — they push sell-in at end of quarter to hit revenue targets, create a sell-through hangover, and get cut from the line the next season.