Wavelets are functions which are form by two resulting coefficients. The detail coefficient and the scale coefficient. From wikipedia Wavelets are defined by the wavelet function ψ(t) (i.e. the mother wavelet) and scaling function φ(t) (also called father wavelet) in the time domain.
The wavelet function is in effect a band-pass filter and scaling it for each level halves its bandwidth.
The scaling and detail basically divide the signal into two applying a high-pass filter resulting into the detail coefficients - (which is the highest level of the transform) and a low-pass filter which results in the scaling coefficients - (which is the lowest level of the transform). This coefficients are calculated for each frequency of the discrete wavelet.
used to for example to extract the deterministic part of a signal and the stockastic part of the signal. They are also used through different procedures to denoise via thresholding the coefficients.