Definition of the word run in

The phrase "run in" originally referred to allowing newly sheared sheep to become accustomed to being shorn, by bringing them into close proximity to the shearing equipment without actually shearing them. This process was called "running them in" in order to reduce the sheep's stress and anxiety during the actual shearing process. Over time, the expression came to mean bringing any animal, object, or event into contact with something else without causing permanent damage or change. For example, "running in" a new sailboat involves taking it out on the water in calm conditions to familiarize crew members with its handling characteristics and to identify any immediate issues. "Running in" new software involves testing it in a controlled environment before implementing it on a broader scale. In each case, the idea is to acclimate the subject to its intended environment in a controlled and gradual manner. The tactic has resulted in the phrase's continued usage, reflecting its inherent utility in diverse contexts.