A rope is a data structure used to represent strings. Ropes are typically implemented with B-trees of (possibly immutable) strings.
The Tk text widget uses a B-tree to store textual data along with tags, so it's some sort of augmented rope, where each node has associated metadata.
Cloverfield suggests that ropes be used in place of flat strings as the primary string representation in Tcl.
See [L1 ] for a real-world implementation of ropes in C ("C Cords").
SGI provides a rope template class in its STL implementation [L2 ].
See also Abstract Data Types.