The location of a substring in a larger string is the position in the string where the substring begins. For example, "CAT" appears in "GCATGATACATG" in locations 2 and 9; "AA" appears in "AAAAA" in locations 1, 2, 3, and 4 (note that the four appearances of the substring overlap).

If a substring of $s$ is written as $s[i;j]$, then its location is simply given by the first index $i$.