 is introduced. The new concept is shown to be distinct from the traditional concept [1]-[3]. various criteria for a given sampling scheme
 is introduced. The new concept is shown to be distinct from the traditional concept [1]-[3]. various criteria for a given sampling scheme  to be alias-free in the new sense are developed. The relationship of the new definition to the question of estimating the spectral density function
 to be alias-free in the new sense are developed. The relationship of the new definition to the question of estimating the spectral density function  of the continuous-time process
 of the continuous-time process  from its samples
 from its samples  is discussed.
 is discussed.