Actually, DISCOM stands for Distribution Companies.

The power sector is categorized into three sections:

• Generation- They generate power by installing the generators.
• Transmission- They get electricity from the generation unit and provides it to the distribution section.
• Distribution- They get electricity from the transmission and manages the further network and distribute the electricity to the consumers. Further accepts payment in terms of electricity bill

• Genco - Generation Companies, Like NHPC, NTPC, Uttar Pradesh Rajya Vidyut Utpadan Nigam Limited
• Transco - Transmission Companies, Like PGCIL, UPPTCL
• Discom - Distribution Companies, Like PVVNL, MVVNL, NDPCL

I wondered for the above reason, why distribution companies were not abbreviated as Disco as transmission and generation companies were named Genco and Transco. Probably, they don't want to get companies misunderstood. Gencom and Transcom could be a better option to sound similar.