Incoterms
Incoterms are the ICC's standard trade terms defining where risk and cost transfer from seller to buyer. They do not set title, payment, or governing law.
Short answer: Incoterms are eleven standard three-letter trade terms published by the International Chamber of Commerce. Each one fixes exactly where the seller's cost and risk end and the buyer's begin. They say nothing about when title passes, how payment works, or which law governs the contract.
Incoterms answer one question precisely: at which point does responsibility move from seller to buyer? Everything else in the sale contract is left alone.
Why they drive landed cost
The term decides which charges you are already paying inside the supplier's price and which land on you separately. Under FOB the supplier's price stops at the origin port rail, so ocean freight and insurance are yours. Under CIF both are already inside the price, and adding them again double-counts your cost.
Why they drive purchase-order closure
Under the F and C terms the seller has performed once the goods are loaded, so the purchase order is satisfied at departure. Under the D terms the seller carries risk to a named destination, so the order is not satisfied until arrival.