The photographic enlarger is a tool used to project a negative onto a piece of photographic paper.
Typically an enlarger is layed out top to bottom as follows:
Light Source - Commonly either a condensor or a diffusion light source. Filter Holder - Puts a contrast filter in the light path (with color enlarger heads this is a little different). Negative Carrier - Keeps the negative flat and positioned in the light path Lens - Focuses the negative onto the stage Stage - Holds the paper being exposed (often in an easel)