Smoke of Deceit:

Smoke of Deceit is a consumable team item that lets heroes move covertly across the map without being revealed by enemy units or most forms of vision until they are very close to enemy heroes or buildings.

It is used to set up ganks, place deep wards, smoke into the enemy jungle, or start fights from an unexpected angle. Its value comes from denying information: opponents cannot safely see a smoked group approaching on the minimap, so they must play more cautiously or risk being caught out of position. For example, a support and two cores may Smoke of Deceit together, walk through the river into the enemy triangle, and catch a farming hero before the other team can react.

Related: Ward, Gank, Fog of war