Standardization assumes that your observations fit a [...] with a well behaved mean and standard deviation. You can still standardize your time series data if this expectation is not met, but you may not get reliable results.
Answer
Gaussian distribution (bell curve)
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Parent (intermediate) annotation
Open it Standardization assumes that your observations fit a Gaussian distribution (bell curve) with a well behaved mean and standard deviation. You can still standardize your time series data if this expectation is not met, but you may not get reliable results.