A pitch deck is a series of slides, 10 to 20, or sometimes more, that a Startup founder uses to present his/ her case in front of investors.

At the bare minimum, it consists of the intro slide, problem statement, the solution, the team, and any metrics, traction etc the project may have gained on launch.

Do a Google search and look for LinkedIn's Series A pitch deck. That's a good place to start. You can also search for tutorials on making a good pitch deck, including how to present it before investors.