Ghosting in poker is an activity during which a player takes advice and input from other players during an active game. In the most extreme of cases, another player will take full control and play the game to the end.
Ghosting is limited to online poker, where it is impossible to know if a player clicking the buttons is acting on their own or if they have help from someone sitting in the room with them or talking to them online.
This practice is particularly widespread in tournaments. One player might make a deep run in a big online tournament like Sunday Million. Say they make the final table where every pay jump matters a lot.
At this point, their friend, coach, or backer will get involved by giving them advice on how to play poker or, sometimes, just taking full control of the account and playing themselves.
The poker community frowns upon ghosting, as it is not fair to other players in the tournament and clearly breaks the “one player per hand” rule that exists and is easily enforced in live poker.