This is an artificial bid to enable you to differentiate a hand with support for partner and fair values from a weak or pre-emptive raise. There are three common situations for playing a value raise:
After partner has overcalled (unassuming cue bid), after partner has opened and the next player has overcalled and after partner has opened and the next hand has doubled.
In the first two cases, the bid to show a value raise is a minimum bid in the opposing suit. In the third case, the bid is 2NT.
For any of the above sequences West might hold: