The two-word thing on which tightrope walkers move is a "tightrope" or "tight wire." It is a thin, tensioned rope or wire stretched between two points, on which the performer walks balancing carefully. The term "tightrope" specifically refers to the firm, tensioned rope that tightrope walkers traverse, and it is distinct from slacklines, which are more elastic and less tense. Tightrope walking is also called funambulism and involves balancing on this narrow support while often using a balancing pole to maintain stability.
