The tracking vocabulary, defined properly.

A tracked event in a shipment's life. The ocean chain runs: empty gate-out → gate-in at origin → ATD → transshipment → ATA → full gate-out → empty return — and each link is something a customer may be waiting on. Milestones are looked up through an identifier hierarchy — booking number → bill of lading number → container number — and the craft of tracking is deciding which milestones matter enough to become a customer update, and which are internal noise.

Estimated vs actual. ETD and ETA are the departure and arrival times the schedule promises; ATD and ATA are the times that actually happened. The distance between E and A is where tracking earns its keep: with global schedule reliability running roughly 59–65% through 2026 (Sea-Intelligence), the estimate is wrong for about one vessel in three. An ETA is a plan, an ATA is a fact — and everything between them is a conversation your customer should hear from you first.

Your container left the hub on a different vessel than booked — bumped by overbooking, a missed connection or a vessel change. Rollovers are usually discovered, not announced: no carrier message arrives; the box simply fails to reload onto the booked vessel. The tell is a discharge event with no matching load, which is why a desk that watches discharge/load pairs at transshipment catches the rollover before the customer books a trucker against a dead ETA.

A scheduled departure the carrier cancelled — the sailing exists on the schedule, then doesn't. Drewry's Cancelled Sailings Tracker put blanked departures at 3–18% of schedules across 2026 windows, with the Transpacific accounting for 46–63% of cancellations. Anything booked on a blanked sailing needs its ETA re-baselined and its people told — the carrier's notice, when it comes, goes to the booking party, not to your customer.

The mid-journey vessel change: the container discharges at a hub port and reloads onto a connecting vessel. It is the riskiest link in the chain — the place rollovers happen and connections slip — and a transshipment delay quietly rewrites the downstream ETA for everyone whose plans were built on the old one.

The per-day charges that start when a container sits inside the terminal beyond its free time. Demurrage is the inside-the-fence clock; detention is its outside twin. Customs holds, late delivery orders and slow pickups all run this meter — which is why exception news has to travel fast: the clock does not wait for the email.

The per-day charges for keeping the carrier's container outside the terminal beyond free time — from full gate-out until the empty is returned. Where demurrage bills the box for sitting inside the fence, detention bills it for staying out too long. The clock stops only at empty return, which makes that unglamorous milestone one of the most financially loaded events in the chain.

The allowance — a set number of days, tariffed or negotiated per carrier and port — before the demurrage or detention clock starts billing. Free time is where exception economics live: a delay that lands inside free time is an inconvenience; the same delay outside it is an invoice. Knowing how much runway each box has left is half of exception triage.

The container leaving the terminal through the gate. Full gate-out at destination means the cargo is finally on a truck — often the milestone the consignee cares about most — and it starts the detention clock. At origin, empty gate-out is the very first event of the chain: the empty box leaving the depot to be stuffed.

The last milestone: the emptied container handed back to the carrier's depot. It closes the shipment's event chain and — critically — stops the detention clock. Missed empty returns are the classic quiet exception: nobody is waiting on cargo anymore, so nobody is watching, while the meter runs.

Proof of delivery — the signed confirmation that the consignee received the cargo, and frequently the document that gates the invoice: many customers' payment clocks start only when the signed POD reaches their accounts team. Paper PODs have historically taken days to weeks to surface (commonly cited at 5–14 days); electronic POD collection is reported to cut days-sales-outstanding by 30–50%, though published ranges vary widely by source — treat specific percentages with care. Either way, a POD that exists on the day of delivery is money arriving sooner.

Where Is My Order — e-commerce's name for the status question, benchmarked at 20–40% of retail support tickets at roughly $5 per contact (retail figures; freight's version has no public benchmark yet). Freight has the same disease without the acronym: the where-is-my-container WhatsApp storm, named by TMS vendors as a churn driver. The cure is the same in both worlds — the update that lands before the question.

The manual status call — to a carrier line, a terminal or a driver — to find out where a shipment actually is. Circulating figures put check calls at 40% of an operator's time and 60–80 calls per coordinator per day, but note the provenance: those numbers are vendor-published with a McKinsey attribution whose primary source we could not locate. Treat them as directional; the hours are real even where the citation is soft.

The air waybill is airfreight's transport document and its tracking identifier. The Master Air Waybill (MAWB) sits between forwarder and airline; the House Air Waybill (HAWB) between forwarder and customer. Air shipments are tracked against the AWB number the way ocean boxes are tracked down the booking → BL → container hierarchy.

IATA's standard air cargo status messages (Freight Status Update). The canonical chain: RCS (received from shipper) → MAN (manifested) → DEP (departed) → ARR (arrived) → RCF (received from flight) → NFD (notified for delivery) → DLV (delivered). In practice the feed is patchy — one air-cargo software vendor (Riege) puts 40–60% of FSU milestones missing — which makes raw air tracking data worse than ocean, not better.

The air cargo quality concept popularised by Cargo iQ: did the shipment actually move on the flights it was planned onto? It is air's counterpart to catching a rollover — a shipment can arrive and still not have flown as booked, and the FSU trail is where that shows. Cargo iQ maintains the formal specification; verify the exact definition at cargoiq.org before citing it anywhere contractual.

The industry's headline on-time metric: the share of vessel arrivals that hit schedule, published monthly by Sea-Intelligence. Through 2026 it has run between 59.0% and 64.7% — roughly one vessel in three arriving late, averaging about 5.2–5.5 days late when it does. It is the single number that explains why tracking is a communication job: the schedule itself is only about two-thirds true.

India's import manifest: filed electronically on ICEGATE by the carrier — not the importer — under Section 30 of the Customs Act, listing every consignment on the conveyance with a line number per bill of lading. The Bill of Entry must match that IGM number and line number; a mismatch locks the cargo until amended. For India-bound shipments, “has the IGM been filed, and what's my line number?” is a milestone in its own right.