This is the 3587th most frequent German word.
mist
Manure; dung; rubbish; nonsense.
Here, 'Mist' is used colloquially to mean 'rubbish' or something of low quality.
Diese Idee ist echt Mist.
This idea is really rubbish.
In this context, 'Mist' refers to 'manure,' related to agriculture.
Der Bauer hat Mist auf das Feld gebracht.
The farmer spread manure on the field.
Here, 'Mist' is an exclamation expressing frustration or annoyance, akin to saying 'Darn!' in English.