Silence is a debuff that prevents item and ability use. Silences can be removed by being inflicted with Debuff Immunity. However, Silences will not be removed-- for example, if you are Lord.Zyrkhan and enter Overdrive [Q-- grants Debuff Immunity and Movespeed as well as reducing collision radius to 0], you can be silenced and rendered incapable of using your spells. However, if you are silenced and possess a Parallax Generator, you can [if you get lucky] remove the Silence when the Debuff Immunity is freshly applied-- the same happens if Balrog uses his Screech [W] skill while near a silenced ally.
Silences do not affect Passive Abilities nor Passive Effects from items.