Sprue comes from a dutch word spruw describing a chronic disease characterized by defective absorption of food.....Thankfully someone sometime ago redefined it to refer to the casting process.
The sprue is the largish channel that allows crazy hot molten metal to travel to and through gates, runners and a pattern without (hopefully) allowing gas in, temperature loss, metal starvation(?for real?) or investment erosion to occur.
If all that happens and there isn't too much turbulence, porosity, or shrinkage of solidification, the jeweler gets a casting tree. That is the funny little statue that has numerous parts and pieces of a cast on it aka the beginning of your new piece of jewelry.
The Art of Custom Jewelry is practiced daily @The Golden Buffalo®