Hi Ayan,

Do you mean the sample mean notation? There are quite a few notations for the sample mean. M or m is a common notation that is used. Often, if x is the variable in the sample,  putting a bar (?) over the x would indicate the mean of the variables. Unfortunately, I cannot create the exact character here, but it is just x with a line drawn horizontally above it.

The word "natation" means swimming. Does that make any sense in the context you found it in? For example, are you working on a problem that has to do with swimming?

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