BP	Bad Processing
CNC	Computerised Numerical Control
DFT	Discrete Fourier Transform
DWT	Discrete Wavelet Transform
EEMD	Ensemble Empirical Mode Decomposition
ELM	Extreme Learning Machines
EMD	Empirical Mode Decomposition
FDA	Frequency-Domain Analysis
FFT	Fast Fourier Transform
GP	Good Processing
HHT	Hilbert–Huang Transform
IMF	Intrinsic Mode Function
IMS	Intelligent Maintenance Systems
MEMS	Microelectromechanical systems
MF	Median Frequency
OP	Different operational segments
PSD	Power Spectral Density
REB	Rolling element bearings
SSA	Singular Spectrum Analysis
STFT	Short-Time Fourier Transform
TDA	Time-Domain Analysis
TFA	Time–Frequency-Domain Analysis
WP	Welch periodogram
WPD	Wavelet Packet Decomposition
WPT	Wavelet Packet Transform