I was reading Bloch's conjecture for projective algebraic curvers(algebraic curves that are homogenous, for example $x^2+y^2-z^2=0$), and stumbled across this notation, $p_g(X)$. What does this denotion mean? I was first thinking it would be the vanishing of the Albanese kernel, but it is sadly conjectural only. Thanks for all your answers.
Let $X$ be a curve (e.g. an integral scheme o dimension 1, proper over the base field, all of whose local rings are regular; such a curve is projective). Then $p_g(X)$ denotes its geometric genus, which is also equal to the arithmetic genus. Thus we talk about the genus $g=p_g(X)$ of the curve, which is the quantity appearing in the Riemann-Roch Theorem.