1. Take an insufficient number of samples
   "The survey undersampled rural populations, skewing the results"
    
2. (signal processing) sample a signal at below the Nyquist rate
   "Undersampling the audio signal resulted in aliasing artifacts"
    
3. (machine learning) remove samples from a majority class to make the full sample more balanced between classes
   "They undersampled the majority class to address the imbalanced dataset problem."

Derived forms: undersampling, undersamples, undersampled