An After Effects project is a single file that stores compositions and references to all of the source files used by footage items in that project. Compositions are collections of layers. Many layers use footage items (such as movies or still images) as a source, though some layers—such as shape layers and text layers—contain graphics that you create within After Effects.
A project file has the filename extension .aep or .aepx. A project file with the .aep filename extension is a binary project file. A project file with the .aepx filename extension is a text-based XML project file.
The name of the current project appears at the top of the application window.
A template project file has the filename extension .aet. (See Template projects and example projects.)