Posters are set up around the room and small groups of students go from station to station together responding to a prompt. These prompts will result in the small groups having conversations. Also can be called Chat stations.
In some cases students create posters and give short presentations and have a Q&A about it afterwards. Other times the teacher prepares discussion prompts that are set up around the room for students to go to in their small groups.
It's a good way for students to have a conversation in a small group so everyone gets a chance to speak and students are more comfortable speaking to less people. Also moving around the room keeps the students active and alert to what is going on.
The teacher might not get to oversee all of the conversations that go on in the small groups for each station that is around the room. The students might not be participating in the discussion or talking about things other than the topic.