I think the metro distinction is often frequency of trains and usage of the tracks. Ie London runs trains every 2 mins basically from 6am - 8pm on virtually eve

I think the metro distinction is often frequency of trains and usage of the tracks. Ie London runs trains every 2 mins basically from 6am - 8pm on virtually every line vs a heavy suburban rail which will run every 15 - 30 mins, share track with freight or intercity rail and so on. I know it doesn't look too different to a passenger but operationally I think they are very different.