The word silo originally referred to grain or missile storage containers, but is now used as a metaphor to refer to separate entities that store information and effectively seal it. In business, organizational silos refer to business divisions that operate independently and avoid sharing information. In fact, it's a very good metaphor. Rural silo banks, often high and dominant, parallel, side by side but sealed from each other, represent isolated upward hierarchies in a company's pit.
The idea of silos in organizations seeks to evoke an image of employees isolated from each other, just as different types of grains are isolated in their silos. The thing about grain in silos is that grain has no legs that can take it to visit other silos. To understand organizational behavior, the term silo mindset often refers to a mindset that creates and maintains information silos within an organization.