What does the W mean in the description of an attack power in DnD 4e?

Answer 1

The [W] in a description like '3[W] + Strength modifier' represents the die or dice you would normally roll for damage with the weapon or attack. In this case, you would triple the number of dice and add your character's strength modifier stat to get the final result.

If damage is normally 1d6, roll 3d6 instead.

If damage is normally 2d4, roll 6d4 instead.

The standard dice notation of 1d6 means one 6-sided die, 2d4 means two 4-sided dice, and so on.