SVM	Support vector machine
TCM	Tool condition monitoring
MCU	Microcontroller
ML	Machine learning
RF	Random forest
RBF	Radial Basis Function
MAPE	Mean absolute percentage error
L&T	Longitudinal and torsional composite vibrational mode
CAD	Computer aided design
Lf	Free length of the end mill (mm)
FEM	Finite element method
PZT	Piezoelectric transducer
OD	Outer diameter (mm)
ID	Inner diameter (mm)
H	Height (mm)
PCBA	Printed circuit board assembly
MCU	Microcontroller
DC	Direct current
3D	Three dimensional
CNC	Computerized numerical control
HSS	High speed steel
n	Spindle speed (RPM)
vf	Feed seed (mm/min)
fz	Feed per tooth (mm/tooth)
ap	Axial depth of cut (mm)
ae	Radial depth of cut
uK, uN	node displacement vectors
M	Mass matrix
K	Stiffness matrix
C	Damping matrix
α	Mass proportional damping coefficient
β	Stiffness proportional damping coefficient
C	Carbon (%)
Si	Silicon (%)
Mn	Manganese (%)
Ni	Nickel (%)
P	Phosphorus (%)
S	Sulfur (%)
Cr	Chromium (%)
Mo	Molybdenum (%)
Ra	Arithmetic mean roughness (µm)
Avg	Average value of the capacitor charge level values
Var	Variability value of the capacitor charge level values
Sd	Standard deviation of the capacitor charge level values
ACorr	Autocorrelation value of the capacitor charge level values
M 4 Avg	4 data point simple moving averages of the capacitor charge level
InterQ	Interquartile value of the capacitor charge level values
Energy	Absolute energy of the capacitor charge level values
ACF	Autocorrelation function
MAF	Moving average formula
k	Time interval
Q	Quantile function
Q 1	First quartile
Q 4	Fourth quartile
p	Probability value (0 < p < 1)
r	Negative correlation
$R^2$	Coefficient of determination (0 < $R^2$ ≤ 1)
SSR	Sum of squares of residuals
SST	Total sum of squares
$\widehat{y_i}$	The predicted value
$\overline{y}$	The mean value
$PtoP$	Peak-to-peak
MAPE	The root mean square error
STDL	Seasonal-Trend decomposition by losses
$T_t$	Trend component
$S_t$	Seasonal component
$R_t$	Irregular
SE	Shannon entropy
$\hat{f}\left(\lambda \right)$	Estimate of the spectral density of data