Sinister: What is Tigermilk?

Hello all, What is Tigermilk? I hear you all mentioning it all the time and I can hear you all scroning me for not knowing - "What is Tigermilk!, How dare he associate himself with Belle & Sebastian without knowing ". I am, however, fairly new on the B&S scene and all I have heard so far is "If your'e feeling sinister" and I know nothing. So plase don't turn your back on me for this and remember no one was born with the knowledge. Any other recommendations would also be apreciated. tata, Huw