# How to distinguish between the different frequency domains?

Sometimes the terms 'Fourier domain', 'complex frequency domain', 'Frequency domain' and 's domain' are used interchangeably.

Take those answers here for example: http://answers.yahoo.com/question/index?qid=20090924230321AAxvnJg

Can you really use them interchangeably all the time, without being technically wrong? So, could you describe what would be wrong if I would replace 's domain' by 'fourier domain' for example? Or replacing 'complex frequency domain' by 'frequency domain'?

## migrated from scicomp.stackexchange.comApr 21 '13 at 18:36

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For Laplace transforms, "s domain" will work as well, and I do believe they are interchangeable. I do not believe "Fourier domain" would be correct usage in this case. "s domain" may be preferred if you wish to emphasize that real values of $s$ have a clear aperiodic interpretation (exponentials in the time domain).