It is probably easiest (and fastest) if you just ask specific questions rather than wait for someone to compose a universal dictionary
For starters, have a look at this post:
http://www.insimenator.org/showpost.php?p=79121&postcount=3This will explain the fundamental differences between mesh and texture. Skinning is the process of applying geometry(mesh) to a skeleton. In the post above, the skeletal joints are represented by the dark blue circles. If you were to draw lines between the joints (sometimes called bones), it would form the skeleton or frame around which the mesh is composed. The individual vertices of the mesh are attached to one or more joints. When an animation runs, the animation moves the positions of the joints, and the vertices of the mesh that are attached to those joints move with it...just like the skin of your own body stretches and bends in response to your bones moving. This process is called skinning. In Sims2-speak, sometimes the term "skinning" is used generally to mean both meshing and texturing (described below).
Texturing is the process of applying 2D textures (or new textures) to a mesh. In the above example, the image of the sweatpants and top are applied to the polygons of the mesh to make a completed image. When you retexture an object, you are replacing someone else's texture and replacing it with your own and applying it to the same geometry.
UV mapping is the means by which a texture is applied to a mesh. It's a way of correlating an area of the texture to a location on the mesh...it is a means of saying that this region of the texture is to be applied to the hands, and another area is applied to the breasts, and another area is applied to legs, and so on. UV mapping is what creates the relationship - or binding - between regions on a texture to polygons on the mesh. If all you're doing is retexturing an existing mesh (like creating custom clothing), then the UV mapping has already been done for you in most cases. Only if you are creating a new mesh with new textures do you really need to concern yourself with UV mapping. This is a fairly advanced topic, and not something most people need to trouble themselves with.
Hope this helps. If you have further questions, feel free to ask.
J