error level : Also known as the error ratio, the error level (
a) represents the number of errors allowed per character of text to
be searched(k/m). This ratio can be used in analyzing the
performance of a string algorithm.
filtration algorithm : In the case of text searching, filtration algorithms
proceed by quickly discarding large text areas that cannot contain a match
to the pattern being searched for, and verifies candidate areas using a classical
string matching algorithm.