How do you define cliché in your own words?

The definitions offering are actually missing something here:

A clichéd expression is an expression that was figurative or otherwise had rhetorical potency—but which has become deprecated by stylists in a language community, because they value novelty and freshness over familiarity and conventionality in discourse. This is a cultural judgement, and one that English-language culture in particular is more prone to than others.

The bits that need to be emphasised:

• was figurative or otherwise had rhetorical potency: not just any phrase, but a phrase that used to be potent. Simon Hayes had it as pithy.
• become deprecated by stylists in a language community. Not necessarily by everyone else in that community!
• This is a cultural judgement. Many language communities are nowhere near as averse to clichés. In fact, it’s a judgement call: not all our discourse can be innovative 100% of the time, and formulaic expressions are necessary. Do you really want to be switched on while speaking 24/7?

As Bartek “asdjklasdjkl” Król has pointed out, the term has been extended from phrases to tropes and scenarios in media and artistic expression. Again, this is a cultural judgement.