Photoshop is a tool that helps people change pictures. It's like having magic powers to change the way things look on a picture. For example, you can make someone look bigger or smaller, change the color of the sky, or remove something that you don't want in the picture.
When people say they "photoshopped" a picture, it means they used this tool to make changes to it. It's like using a crayon to draw on a picture, only what you draw with Photoshop can be much more complex and realistic.
Photoshop is mostly used by people who work with pictures a lot, like photographers, designers, and artists. But anyone can learn how to use it if they want to make their pictures look a certain way.