What does the "'operator<' error mean when using operator overloading for the sort() function on a vector?

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The "operator<" error occurs when the overloaded comparison operator used in the sort() function for a vector is not defined properly or is missing. The sort() function needs to know how to compare the elements in the vector to be able to sort them. If the comparison operator is not properly overloaded, the function will be unable to compare the elements and sort the vector.