A longest common substring of a collection of strings is a common substring (i.e., a shared substring) of maximum length. For example, "CG" is a common substring of "ACGTACGT" and "AACCGGTATA", but it is not as long as possible; in this case, "GTA" is a longest common substring of "ACGTACGT" and "AACCGTATA".
The longest common substring of a collection is not necessarily unique; for a simple example, note that "AA" and "CC" are both longest common substrings of "AACC" and "CCAA".
