Broad gauge, Same as INDB stands for Indore broad gauge. it was due to the meter gauges(INDM - for erstwhile Mhow- Ratlam MG section) and broad gauge platforms situated side by side with adjacent track alignment in three gauge system era,
Sabarmati Viramgam MG section tracks used to run parallely along with BG tracks earlier, hence the nomenclature.
Now this nomenclature has lost significance.