What exactly does 'reveal' mean in this context? Is it meant for something like Spending the Winter Stores or would something like Venomous Blade coming out of shadows trigger this as well?

Text --- Response: After an opponent plays or reveals an attachment,claim 1 power for your House. (Limit 1 per phase.)

You need an effect that specifically shows opponents a card that should otherwise be hidden information without putting it into play. Putting it into play (including bringing it out of Shadows) is an entirely separate mechanic.

Essentially, there is no "implied" reveal effect. The card will use the word "reveal."