What does it mean for a Gamma distribution to have index $\alpha$ and index $\lambda$

Question

I have two easy questions:

1- How is he form of the density of a Gamma distribution with index $\alpha$ and parameter$\lambda$?

2-And if it says "Gamma distribution of mean $a$ and index $b$"?

I know the form of a Gamma distribution but I always hear Gamma with parameters $a$ and $b$, but never heard about this kind of description of Gamma. Could anybody help me please?

Thank you in advance.