Definition
Osmotic communication is the information that flows into the background hearing of members of the team preferably sitting in the same room, where they quickly pick up most relevant information by the Osmosis. When Osmotic communication is in place the questions and answers flow naturally with a little disturbance among the team.
Here indirect information is transferred by overhearing conversation or simply noticing things happening around you, can catch and correct small mistakes before they grow. This way osmotic communication makes the cost of communication low and feedback rate high.
Though Osmotic communication is valuable for all size projects, gradually it becomes slightly difficult to attain as the team size grows.
Further Reading:
http://alistair.cockburn.us/Osmotic+communication/v/slim
https://www.projectmanagement.com/wikis/295442/Osmotic-Communications?forcemobile=on