a large printed picture, photograph, or notice that you stick or pin to a wall or board, usually for decoration or to advertise something

The children put up posters on the classroom walls. 孩子们在教室的墙上张贴了海报。

We noticed a poster advertising a circus. 我们看到一张马戏团演出的海报。

someone who publishes something such as a message or picture on a website or using social media

There was a lively debate on the message boards, with many posters arguing against the plan. 在留言板上辩论很踊跃，许多发帖人反对这项计划。