Mosaics and silvers are NOT the same thing. They are both types of WHITE, yes, but silver is not just another term for or type of mosaic.
And it's not really a selling term either - it is a legitimate variety and show term, although "silver" has definitely been exploited as a selling term.
A mosaic - by definition - is a broken pattern. If you look over the back of any white and see uneven coloration/spots/differing shades/markings/etc (does not include veiling) - it is a broken pattern and therefore a mosaic. Mosaics are
by far the most common type of white.
All the other phases of whites (predominantly white, white with dark guard hair, and silver) have a solid pattern. Looking over the back of a predominantly white, you see nothing but solid white, no dark hairs at all (tails do not count, they can have dark hairs on their tail). A white with dark guard hair will be mostly white but with colored guard hairs (hair that is slightly longer than the rest of the fur). These dark guard hairs are evenly space throughout the coat so the pattern still appears solid.
Silvers are colored evenly over the whole body - they have grey underfur, a visible white bar, and a grey tip over the whole body. Again, tails don't count so a silver can have a solid white tip on the tail and that may be the only factor distinguishing them from a light standard, but no solid white areas or areas where just the tips or just the underfur are colored are allowed on the pelt or it would be considered mosaic. If the coloring looks uneven, like in Spoof's first picture, it's a broken pattern and therefore a mosaic.
The reason for these distinctions (and why tails don't count) is for pelting - because mosaics are broken patterned, they cannot easily be matched with other pelts to make a uniform-appearing garment. The solid patterned whites can be matched more readily, though they're not nearly as common as mosaics.
And the problem with silvers is that a lot of the solid whites are born looking silver, but by the time they're 8-10 months old, they've whitened up so much that they should be considered white with dark guard hair. A silver-appearing kit has to stay silver up until its first prime to be deemed a silver, so when breeders crop up saying they had a silver born, it's not really a valid classification because that kit will lighten up as its adult coat comes in. How much it lightens up can be the difference between silver and white w/dark guard hair.
All that said... here is a silver with parted fur: You can see the grey underfur, white bar (white band between the underfur and tip of every hair) and grey tipping.
If the fur weren't parted and this chin were groomed a bit, you could tell that the back was solid colored - no white or lighter areas except on the tail. Similar to this:
And here is a white with dark guard hair. She probably looked like a standard when she was born, as she does not have a white tipped tail, but she is definitely a white. Just her guard hairs are colored and they are even throughout the coat, so her pattern is solid and she is not a mosaic.
