unary mathematical operator: length/number of components/terms of/in object/array/formal string/sequence/word/text in some alphabet/base/basis which includes each digit; number of digits/components/entries
For a numerical string, the number of digits are counted. For a tuple/vector/array/matrix/tensor, the number of entries/conponents is counted. Not literally the number of symbols used, but the number of meaningful "spots" occupied; for example "(1,0)" uses five characters, but its length is just 2 (for "1" and then "0"); this is due to the fact that formal representation may vary but the amount of information conveyed must remain constant. Note that digit strings are essentially considered to be vectors in the basis of powers of the base.