Silence

Silence is a status effect that prevents those affected from casting spells for the duration of the silence. It can be useful when ganking a hero with a blink or invisibility spell, as silences tend to have longer duration than other disables giving more time to kill the enemy. Silences in team fights can also be very effective even for a short time as they prevent the enemy from using their spell in combination with one another. Silencing an opponent will also stop any channeling spells that they are currently using.

Note that the silenced unit will still be able to use items and their passive skills will be unaffected, except when under the effects of Doom which disables all items and most passive abilities.

Sources of Silence