The term "certain weight" is commonly used in the field of physics, particularly when discussing forces and motion. It refers to a force that produces a constant acceleration on an object or body. In other words, it means that the net force acting upon an object is directly proportional to its mass, resulting in a consistent rate of change in velocity. This concept is often demonstrated through experiments involving inclined planes, where objects are observed to accelerate at a steady rate when subjected to varying forces.