A Thinny is a tear in the fabric of reality, which can lead to other times, parallel worlds or universes.
Wikipedia: Glossary_of_The_Dark_Tower
A thinny is a "weak spot" in reality, where the fabric of reality has been worn thin. They are described as looking like large blobs of mercury and emit a warbling sound similar to a musical saw. This sound can set a person's teeth on edge and/or hypnotize the victim.
Besides the insanity-inducing buzzing and warbling sound, the thinny plays on a person's thoughts; telling them what they want to hear and promising a fine outcome. Death is more likely. Transportation into other universes is possible by simply walking into a thinny, but this is a rare outcome.
In Wizard and Glass the main characters end up passing from All-World into Topeka, Kansas in the world of The Stand by riding Blaine the Mono through a thinny that is breaking between the two worlds. In flashbacks presented in the same novel, Roland encountered a thinny earlier in life that entered into a world filled with monsters that almost "devour" an entire army.
A thinny is a "weak spot" in reality, where the fabric of reality has been worn thin. They are described as looking like large blobs of mercury and emit a warbling sound similar to a musical saw. This sound can set a person's teeth on edge and/or hypnotize the victim.
Besides the insanity-inducing buzzing and warbling sound, the thinny plays on a person's thoughts; telling them what they want to hear and promising a fine outcome. Death is more likely. Transportation into other universes is possible by simply walking into a thinny, but this is a rare outcome.
In Wizard and Glass the main characters end up passing from All-World into Topeka, Kansas in the world of The Stand by riding Blaine the Mono through a thinny that is breaking between the two worlds. In flashbacks presented in the same novel, Roland encountered a thinny earlier in life that entered into a world filled with monsters that almost "devour" an entire army.
by Xzal June 1, 2010
Get the Thinnymug. 
by Delightfol February 28, 2018
Get the Thinnymug. It is a mixture between thin and skinny. A female with no breast, butt or curves. Unattractive probably anorexic. Is the opposite of thick when referring to a female.
by Alism95 March 31, 2017
Get the Thinnymug. by Holly January 1, 2008
Get the thinniemug. "Damn, she's thinny!"
by TrickleMeDown May 20, 2003
Get the thinnymug. by redheadedkillla December 21, 2009
Get the thinnymug.