For the benefit of someone like me who only uses Linux and bash on behalf of myself and the companies I work for and haven't studied it extensively, can anyone

For the benefit of someone like me who only uses Linux and bash on behalf of myself and the companies I work for and haven't studied it extensively, can anyone here tell me what the i is for? I wasn't able to find it in man chmod on my machine, DDG failed me, as did Google. (positive feedback to employees of DDG and Google: whenever I get assigned to the experiment where you show the snippet you thing matches my query it brightens my day, - even if the snippet shows that the result was irrelevant like here "<something about> chmod. I <something about the author>". I think Google used to nail this back in 2007 but anyways, seing the snippet in the front page helps a lot.)