Special Shimano factory cable grease for Shimano SIS cable housing. Apply to cables to keep them corrosion free and moving freely in the housing. A must for any true professional. Expensive, but lasts a long time - buy it once and try and forget how much you paid for it, you'll be happy with the results.
Yeah, it is pricey, but its true, this grease is a amazing. In the past Ive tried lithium grease and also oil. Nothing works like the SIS grease.