There are sections of subway which the train doesn't really run under the ground, but above the ground. How should it be called? Thanks!
In London they're called 'Underground trains', even when they run on the surface. If you need to distinguish, specify 'surface': The District Line is a surface line mostly, but it goes underground near the centre. The smaller ones, which go through circular tunnels, are also called 'Tube Trains' - and people aren't very careful about the size/type of train; you 'take/catch the Tube', even if it's not strictly a tube train
In other cities they're called Metro systems - following the European model. (I don't know which came first, the Paris Metro, or London's Metropolitan Line, which was the first section of the London Underground.