A c-type space is one with more than one link which forms part of a connected sub-system which contains neither type a nor type b spaces, and in which there are exactly the same number of links as spaces. In fact this means that a c-type space must lie on a single ring (though not all spaces on the ring will be c-type) so that cutting a link to a c-type space will automatically reduce the ring to one or more trees.
c-space or c type space
Hillier, B. (1996, 2007), Space is the Machine: A Configurational Theory of Architecture. Space Syntax: London, UK. pp.250