A finite sequence of 
letters from some alphabet is said to be an 
-ary word.
Word
See also
Cubefree Word, List, n-Tuple, Overlapfree Word, Squarefree Word, StringExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Word." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Word.html