I am 100% new to Blender and to the Blender Manual. Could anyone tell me what a blend file is please. It is discussed at length in the manual except for explaining what a blend file is.
The .blend files are the project files of Blender.
They are binary files with the .blend extension as in fileName.blend. Blender saves its data as .blend files and can only open .blend files.
Other 3D files types are not "opened", but imported.
Blend files contain the models, materials, the scene (camera, lights and animation) and the information for rendering and viewing along with the state of the user interface. By default they don't contain images used as textures unless you pack them. Read: How to pack images into blend file
Also not contained as part of the file are simulation caches or the add-on used to create the scene.
a blend file is the extension used in saving a blender data which could be written as .blend popular examples of extension names are .mp3 for music, .jpg for images, .png for images, for blender files we use .blend which contain everything your have created within the software such as meshes, light, world, hdr(s), texture, materials etc.