Shadow banning is the term describing a “hidden ban”. The user still thinks their account is active but their content may not be visible to others. In this example, Twitter is said to be excluding some prominent accounts from search results which has the same effect as a shadow ban.
“We are aware that some accounts are not automatically populating in our search box and shipping a change to address this.” Asked why only conservative Republicans appear to be affected and not liberal Democrats, the spokesperson wrote that “I’d emphasize that our technology is based on account *behavior* not the content of Tweets.”
Source: Twitter is “shadow banning” prominent Republicans like the RNC chair and Trump Jr.’s spokesman – VICE News
Twitter’s shadow ban is hiding the tweets from many members of Congress, prominent staff members, and others.