a diet plan that entails foregoing one's usual meal regimen and replacing it with a substantially meeker allowance of nutriment. Usually such diets last a few days to a week and are implemented prior to an upcoming event that the dieter wants to lose weight for.
Such practices can be unsafe, especially if done frequently, over a longer period of time, or without the appropriate intake of water and nutrients.
I started a crash diet on wednesday so I can fit into my prom dress this weekend.
Stephanie passed out on the field and had to be taken to a hospital; she had been on a crash diet and was undernourished.