There are other martyrs such as those who die drowning, in fire, under a falling building, due to child delivery etc.

The 72 virgins are only for those who are martyred on the battle field.

Is Martyr dead only meant in battlefield or some other type of dead can also be like martyred in battlefield? And does the 72 hoor al-ayn which Allah (SWT) promissed to martyred, is that meant for those who martyr in battlefield?