Lane
Beginner
One high-speed path for data, like one lane on a highway.
Novice
One SerDes channel: a pair of wires (or one fiber, or one color of light) carrying one serial stream, such as 100 Gb/s. A port bundles several lanes: an 800 Gb/s port is often 8 lanes of 100 Gb/s.
Expert
The unit of electrical signaling. Port speed = lanes × lane rate; doubling the lane rate (50 → 100 → 200 Gb/s) halves the lanes per port and the pins per Tb/s, at the cost of reach and equalization power.