For 30 years, the process node number told you the transistor gate length. Then around 2014, physics stopped cooperating — and the numbers became marketing.
Until roughly the 90nm node (mid-2000s), the "node" was the gate length of a transistor — the physical distance electrons had to travel between source and drain. Shrink it, and you get faster switching, lower voltage, more transistors per area. This was Moore's Law working exactly as planned.
Below ~22nm, current started leaking through the gate, and shrinking further stopped delivering the same benefits. Foundries kept the node numbers going for marketing continuity, but the actual feature sizes stopped tracking them.
Today: TSMC's "3nm" node has transistor features closer to ~24nm for the smallest metal pitch, and gate lengths around 16-18nm. The "3" is a naming convention, not a measurement.
Instead of node names, look at transistor density (MTr/mm²) — millions of transistors per square millimeter. TSMC 3nm: ~215 MTr/mm². TSMC 5nm: ~140. This actually tells you how much stuff fits on a chip.
Nobody wants to say "our next chip is on the '22-nanometer-equivalent-density' node." The number is a proxy for progress. As long as everyone agrees to keep the naming consistent, it works — even if it's technically fiction.