Momentum in the physical world is force of something in motion. If something has momentum, it will have a tendency to keep moving (allowing for friction). When a company has momentum, that means that it's success is increasing and will probably continue to do so. If something were to happen to the company - a scandal or mismanagement, say - we would say that the company had lost its momentum. If a company or person has "solid momentum", that means that the their business or success is increasing steadily, not in a stop and go mode.