Don't know what "this" is, but all symmetric distributions are not normal. There are many distributions, discrete and continuous that are not normal. The uniform or binomial distributions are examples of discrete symmetric distibutions that are not normal. The uniform and the beta distribution with equal parameters are examples of a continuous distribution that is not normal.
The uniform distribution can be discrete or continuous.
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It means that the probability density function is symmetric about 0.
The distribution of sample means will not be normal if the number of samples does not reach 30.
It is called a standard normal distribution.
The central limit theorem basically states that for any distribution, the distribution of the sample means approaches a normal distribution as the sample size gets larger and larger. This allows us to use the normal distribution as an approximation to binomial, as long as the number of trials times the probability of success is greater than or equal to 5 and if you use the normal distribution as an approximation, you apply the continuity correction factor.
It need not be if: the number of samples is small; the elements within each sample, and the samples themselves are not selected independently.