The ability to weigh up factual information and decide on a course of action based on that judgement. That’s how I would define reason. The difficulty arises when you try to establish factual information. The search for objective truths is never easy, particularly when inaccurate or false information is so easily disseminated.
If the President of the United States of America can get away with obvious falsehoods (do you remember his advice to drink bleach to cure Covid) who knows what nonsense is being trotted out by so called experts. We all know that politics is a dirty game and Trump knows how to sling dirt at his opponents. Who cares if his filth is unverifiable or obviously false, there will be people who swallow his falsehoods and repeat them.
Science doesn’t always get it right first time. Blood letting is a practice that has thankfully ceased and frontal lobotomies are rarely performed. Lets not forget that Galileo could not observe that the Earth orbits the Sun without fear of excommunication.
I am reminded of the soundtrack to the film O Lucky Man written by Alan Price…
if you’ve found the reason to live on and not to die you are a lucky man…
https://music.youtube.com/watch?v=wVku7XDtMkY&si=CAizm1f1rfODXtoa
Albert Camus had much the same philosophy about finding a reason for living.
There is also the ‘reasonable man’s test in English law. This test uses the example of a man on the Clapham omnibus to illustrate what Joe public would think about a given situation.