“Hedging” refers to taking an offsetting position on the same instrument.
You can fully hedge one position if you open a new one that fully offsets the existing one; (you open 5 Lots of EURUSD long to cover the existing 5 Lots of EURUSD short) or partially hedge when the new position offsets part of the existing; (open 3 Lots of EUR/USD long to hedge part of the existing 5 EURUSD Lots short).
The “Hedging” is used to reduce the risk of one position. On the AvaTradeACT platform no margin is required to hedge a trade. The MetaTrader 4 system requires enough free margin to cover the spread cost.