The name means five waters. Indian Punjab has parts of three rivers and Pakistani Punjab has parts of four, and no political unit called Punjab has five.
Indian Punjab is about fifty thousand square kilometres, an eighth of the province of 1901, with about thirty million people.
Pakistani Punjab is about two hundred and five thousand square kilometres with about a hundred and twenty-seven million people, more than most countries.
The name is used by both and by everyone who left either.
It describes a language, a food, a set of manners, a way of holding a wedding and a way of arguing, and it survives the fact that there is no Punjab in the sense the word originally had.
That is a reasonable definition of a region as against a state: something that persists after the administrative unit that carried its name has been divided twice and reduced by seven-eighths.
The name is Persian and dates from the Mughal period. It describes an administrative province rather than a linguistic region, and the two have not coincided since 1947.
Indian Punjab has two and a half of the five rivers. The Beas and the Sutlej run through it, the Ravi forms part of its boundary, and the Chenab and the Jhelum are entirely in Pakistan.
What holds the meaning now is the language and not the water. A Punjabi is somebody who speaks it, wherever the rivers are.