Parameters refer to characteristics of a population, while statistics refer to characteristics of a sample. Population parameters are commonly denoted by Greek letters, sample statistics by English letters.

正確答案是：D: It is a population parameter, commonly denoted by the Greek letter mu μ。

專(zhuān)業(yè)分析：
在統(tǒng)計(jì)學(xué)中，研究一個(gè)國(guó)家成年男性的平均體重屬于對(duì)總體（population）的研究?？傮w參數(shù)（population parameter）是描述總體特征的數(shù)值，而樣本統(tǒng)計(jì)量（sample statistic）是描述樣本特征的數(shù)值。

選項(xiàng)分析：
A: It is a population statistic, commonly denoted by the Greek letter mu μ
- 錯(cuò)誤?？傮w參數(shù)用來(lái)描述總體特征，而不是總體統(tǒng)計(jì)量。

B: It is a population parameter, commonly denoted by the letter s
- 錯(cuò)誤?？傮w參數(shù)確實(shí)是描述總體特征的，但“s”通常用于表示樣本標(biāo)準(zhǔn)差，而不是總體平均值。

C: It is a sample statistic, commonly denoted by the Greek letter mu μ
- 錯(cuò)誤。樣本統(tǒng)計(jì)量描述的是樣本特征，而不是總體特征，而且樣本平均值通常用 \(\overline{x}\) 表示，而不是 μ。

D: It is a population parameter, commonly denoted by the Greek letter mu μ
- 正確?？傮w平均值（即總體參數(shù)）通常用希臘字母 μ 表示。

因此，D 選項(xiàng)是正確的答案。