This business concept, especially the term, is inspired by safety practices observed on construction sites.
The general idea of this concept is to identify and set a certain level of working capital, selling price, production level, etc. to better manage business variables. The goal of setting a Safety Net is to ensure business progress and resiliency during critical times such as financial set back, unfavorable market condition, or tight competition. Safety Net is usually a little over the break-even point.
Though this concept is normally used on business planning, this also serves an important role on personal financial management. In fact, the idea of saving 3 - 6 months worth of Cost of Living is based on this concept.