Osmosis training is one of the names given to the small amount of training all players received, if they didn't play in the correct position for that training type or if they didn't play at all. In the table in Chapter 17 of the rules, this was indicated by "((others))". Note that players don't receive this training with goalkeeping training. This small amount of training is estimated to be around 1/6 of the training a player receives when he played on the right position for that training type.
Some managers try to profit from this phenomenon by buying a lot of players with a very high sub-level. If done correctly the small amount of training will do to make a player pop within a couple of weeks. Then the player will be sold for a profit, which is a type of skill trading. In November 2007, this training was limited to players that played in a match that week. Previously, all players on a squad received training. However, it takes considerable skill and experience from the manager to spot players with a sufficient high sub level in the first place and to make a good profit trading them.
The term osmosis training is somewhat of a take-off on the "learning by osmosis" joke where someone puts a book on his head and the knowledge is transported from the region of high concentration, the book, to the region of low concentration, the head. The process of such transportation through a thin membrane is known in biology and physics as osmosis. Of course the carry-over training isn't exactly the same thing, certainly, but the conceptual similarity is there.
Osmosis training is also known by several other names, including
Shadow Training (English) : Since the players given osmosis training "shadow" the players getting the main training.
Fusion Training (English) : Because of its nice sounding.
Residual Training (English) : Fairly straightforward name. A residual is the amount left over after a process.
Klaverjas Training (Dutch) : Derived from a cardgame that was popular among professional players in the Netherlands. It was played to kill time during training camps and long busrides. The players used to bet quite heavily on the cards. As not everyone could stand losing or felt obliged to pay his debts, this sometimes resulted in a bit of tension, even to the extent that players were forbidden to play klaverjas anymore by their coaches. Since players bought for the sole purpose of receiving osmosis training only sit around in the canteen or on the bench, they have plenty of time for cardgames. Also due to the frequent transfers and subsequent TS-drops, the team spirit would suffer from this cardplaying bunch of guys. Therefore the link with the cardplaying incidents was easily made.