As an editor I often encounter the symbol $g_r^d$$g_d^r$ as a noun. I tried googling but I only get papers where the symbol is used without a definition. Can someone supply a reference to a definition? Examples of usage: "Koszul cohomology groups of $g_d^r$s on singular nodal curves"; "any other basepoint-free $g_h^1$ [...] is composed with the given $g_d^1$.