EMC or Energy Matter Covalence is a mechanic from Equivalent Exchange 2. This is the energy that is used in everything within the Equivalent Exchange 2 mod. Almost everything in Minecraft has an EMC value, allowing them to be transmuted into each other. EMC can be created artificially with Energy Collectors and Anti-Matter Relays. It can be stored in Klein Stars.
Items with EMC values will be stated in their tooltips when Equivalent Exchange 2 is installed.