What is the difference between random.normalvariate() and random.gauss() in python?

What is the difference between random.normalvariate() and random.gauss() ?

They take the same parameters and return the same value, performing essentially the same function.

I understand from a previous answer that random.gauss() is not thread safe, but what does this mean in this context? Why should a programmer care about this? Alternatively posed, why was both a thread safe and non-thread safe version of included in Python's 'random'?