In mathematical objectivity, a string (or 1-brane, or, more formally - a 1-dimensional object occupying some metric space) is an arbitrarily one-dimensional (1d) curvilinear path integral (integrand) with (at most) two (2) endpoints (in/input and out/output) called nuts. Strings may be open🔓 or closed🔒, but not both. (see brane, SMALL brane, loopstring➿, string ludology, thread, walk)
Computationally, a string is a stream (sequence) of preimages (ie. a concatenation of flageolet pencils).