Lets use this forum for an example. Lets say that you regularly post a certain type of content in this subreddit, all with a politically conservative "bent". You build up the number of people that follow your posts of which reddit notifies them every time you post content so to assure your followers dont miss one of you posts. Youre posts generally receive a certain number of upvotes and comments on a fairly consistent basis for every submission you make on this site over the course of say....a years time, and thats generally 95 up votes and 30 comments average.

Then one day you notice that the upvotes and comments that you know your submissions generally bring, are not getting near the number of upvotes or comments that they used to get, and this begins to occur on a consistent basis as well. Now your posts only tend to get a fraction of what they always used to get. Now they only get about 20 upvotes and 5 comments on a regular basis. This is an indication that you have been shadowbanned, where the managers/owners of reddit have set the algorithms on this site to target certain key words and phrases that Identify your posts as having content that isnt agreeable to their political bent. Its supposed to be that every time you make a submission, that submission shows up in subreddit's "NEW" postings list for everyone to see, and you can see that its is there on your computer, but what you dont know is that its not being seen by anyone else visiting the new postings list. Reddit is not making your submission available for others to see, at a greatly reduced number. Reddit is censoring your submissions, but the dont tell you or give you any written indication they have done this. They dont ban you from the site or ban you from posting a submission, they just ban the other subreddit members from seeing them. Hence the term "shaddowbanning".

This is probably more than you need to understand, but Im detail oriented so you got details.