Friction is a psychological resistance to a given element in the sales or sign-up process. Anxiety is a psychological concern stimulated by a given element in the sales or sign-up process. Reduce these as much as possible and watch your sales go up. Absence of trust is also friction - a visitor will not convert if he doesn't have confidence or trust in you.

You cannot eliminate friction - whenever you ask money for your products or services, there's always friction. But you can and should minimize it.