* Malapropism: This refers to the misuse of a word for one that sounds similar, often resulting in a humorous effect. While not directly related to your example, it involves using the wrong word, which can lead to an irrelevant description.
* Idiom: This is a phrase that has a figurative meaning that is different from the literal meaning of the words. Saying "rack up mileage" to describe walking is an idiom, as the literal meaning of "rack up mileage" refers to accumulating miles in a vehicle, but it is used figuratively to describe physical activity.
* Figurative language: This is a broad term that includes metaphors, similes, and other ways of using language to create a particular effect. While not specifically about irrelevancy, using figurative language can sometimes lead to descriptions that are not literally true.
* Slang: This is informal language that is often used within a particular group of people. Slang phrases can sometimes be used in ways that are irrelevant to their literal meaning.
* Jargon: This is specialized language that is used within a particular profession or field. Jargon can sometimes be used in ways that are irrelevant to people outside of that field.
* Miscommunication: This is simply a failure to understand each other, which can happen when someone uses language in a way that is not clear or understood by the other person.
Ultimately, the best way to describe the use of an irrelevant phrase depends on the specific context and the intended meaning.