So I was just given the definition of a signature:
A signature is a pair $\Sigma = (\Omega, \Pi)$ where $\Omega$ is a set of operation symbols $\omega$, each equipped with an arity $\alpha(\omega)\in\mathbb{N}$ and $\Pi$ is a set of relation symbols $\pi$, each equipped with an arity $\alpha(\pi)\in\mathbb{N}$.
And I saw the term "first order signature" after this without any previous context. Can anyone tell me what is a "first order signature"? Thanks a lot.