Here's how google explains it.

At a conference, a poster presentation involves displaying your research or project on a large, visually-rich poster, followed by an informal discussion with attendees who stop by to learn more.

Here's a more detailed explanation:

What it is:

A poster presentation is a way to showcase your work in a concise, visual format, often used in academic and professional conferences.

How it works:

You create a poster summarizing your research, including visuals like graphs, tables, and images, and then stand by your poster during the designated session to answer questions and discuss your work.
Informal and Interactive:
Poster sessions are typically more informal than formal presentations, allowing for relaxed discussions and networking opportunities.

Benefits:

Showcase Research: It's a great way to present your work to a wider audience and receive feedback.
Networking: Poster sessions provide opportunities to connect with colleagues and potential collaborators.
Learning: You can learn about other people's research by browsing different posters.
Low-Stakes Format: It's a less intense way to present your work compared to a formal presentation.

Preparing for a Poster Presentation:

Design: Create a visually appealing and informative poster that summarizes your research clearly.
Content: Include key findings, methods, and conclusions in a concise and easy-to-understand manner.
Practice: Prepare a brief overview of your research to share with attendees.
Engagement: Be prepared to answer questions and engage in discussions about your work.
Comfort: Wear comfortable shoes, as you'll be standing for an extended period.