A cliche in general is referring to something that has been used or heard numerous times. A minor cliche in music is using a descending (more common) or ascending (relatively rare) chromatic lines within the chord harmony to create a melodic movement pleasing to the ears. This idea is used in many different songs, notably Something by Beatles, Stairway to Heaven by Led Zeppelin etc.
The most common example of a minor line cliché, is the descending chromatic line that comes down from the root of a minor triad. Since we can play minor triads all over the neck in any inversion and on any set of strings, both open and closed positions, we can start this cliché in many places and with many fingerings.
The ascending minor line cliche is also often referred to as ‘James Bond’ line cliche. Listen to the theme song of James Bond to see if you can hear why it is called that 🙂