What is the gamma term in the modified Bessel function of second kind of Order Zero?

Question

In my version of Schaums mathematical handbook (4th edition page 156), it gives the following for $K_0$

$$ K_0= -\big(ln(x/2)+\gamma\Big) I_0(x)+\frac{x^2}{2}+\frac{x^4}{2^2\cdot4^2}\left(1+\frac{1}{2}\right)+\frac{x^6}{2^2\cdot4^2\cdot6^2}\left(1+\frac{1}{2}+\frac{1}{3}\right)+... $$

But it doesn't define what $\gamma$ is.

Is $\gamma$ some arbitrary constant?

Answer 1

$\gamma$ is the Euler-Mascheroni constant.