technically, if you alter one pixel then it's a manipulation. however, there is another use of that term that is used also and much more common. there are classes of alterations in digital. you have 'retouching', 'restoration', 'reconstruction', 'photo-art', 'colorization', and 'manipulations'. each of these has its own characteristics. yes, they could all be called manipulations, technically. but mechanically, there are differences.
a retouch is usually to correct some minor fault, either in the picture taking or in the subject matter. the lighting was a bit off, the subject had a pimple, and small things like this.
a restoration is usually a bit more extensive and has another purpose, to bring an image back to its original state. this involves remove mold, scratches, dust marks, textures, and so on. it generally is also only removing unwanted things but on a larger scale to restore an original.
reconstruction often is lumped into the same category as restoring. i make the distinction that when pieces of the image are actually missing then it's a reconstruction. a corner is gone, large tear marks exist and parts of the data are no longer there and so on.
photo-art is the manipulation with the intent of altering the image into something more or differently aesthetic, or with the intent of telling a better story. it often involves filters and brushes and techniques designed to do just that.
colorization is simply that, colorizing the image either further than what it already is or turning it newly into a color image.
manipulation is the act of interjecting new items or removing existing items from an image. so, if i put a puppy into the picture with the baby, that's a manipulation. likewise if i remove aunt may from the baby picture, that's a manipulation.
now, none of those definitions are necessarily ever 'pure'. sure, there's overlap. and sure more than one defined item may get used in a single image. so, you remove aunt may, add the ball, change the contrast, fix a blown out area, put some texture back in baby's face and so on and so on. so, some images are going to be composites of techniques and classes. that's ok. as to how you class a single image and therefore sort and post and store it, may be a bit of a trick at times. but, as long as you can justify it in at least one correct class, then it's really not going to make that much difference.
we get folks wanting 'critiques' posting in the 'help wanted' section. well, they want help, so it fits. or someone will post a notice about a piece of retouching software in the retouching forum rather than the software forum. well, it does apply to retouching, so it's not totally out of place. though, i'd rather have all software related links in one place for easy finding.
and, most forum software also has the ability to move a thread without removing. i forget what it's called, but basically the thread is still listed in the forum in which it was originally posted, but when you click on it and then back out of it, you now find yourself in another forum where it was link-moved (or whatever it's called). or, you can actually move it.
so, dont get too hung up in the semantics of it all. we all love a good picture, no matter where it's stored
Craig