For questions related to Euler's constant $\gamma$, which is defined to be the limiting difference between the natural logarithm and the harmonic series.
Euler's constant, also called the Euler-Mascheroni constant and typically denoted $\gamma$, is defined to be the limiting difference between the natural logarithm and the harmonic numbers:
$$\gamma=\lim_{n \to \infty}H_n-\log n$$ where
$$H_n=1+\frac{1}{2}+\cdots+\frac{1}{n}$$
Euler's constant arises in analysis and number theory, in part due to its connections with the gamma and zeta functions.
Note this is not the same as Euler's number $e$, defined by $e:=\sum_{n=0}^{\infty}\frac{1}{n!}$. Questions about this number should use the tag eulers-number-e.
Source: the Wikipedia article on the Euler-Mascheroni constant.
