PCIe lane
Beginner
One set of PCIe wires. It works like a two-way road, with one side for sending and one for receiving.
Novice
The basic unit of a PCIe link: two differential pairs, one per direction, so a lane sends and receives at the same time. A “x16” link bundles 16 lanes and has 16 times the bandwidth of one.
Expert
One transmit and one receive differential pair, each carrying the full per-lane rate (for example 32 GT/s at PCIe 5.0). A x16 link therefore has 64 signal wires. Lanes are the scarce resource on a CPU package and a board: the lane budget.
Explained in Board and server (Systems).
See also: PCIe (PCI Express), Link width (x1–x16).