Emu Means Electric Multiple Unit which runs in major suburban sections where stations are closer to each other.. EMU are Designed to run at higher density suburban sections with more acceleration and deceleration power than a memu. A EMU can run maximum 150 km. ( not sure about the distance)
Memu means Mainline Electric Multiple unit which runs through main line between various important town and section than the major sub urban section.
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Like Bwn Asn memu , Adra asn memu .
Memu can clock 200+ km in one go . Example Asn varanasi memu , Bwn - Bksc Memu.
You can find more details on faq section. Have a look there.