This is a term you'll hear often. It is used as both a verb and a noun. Discovery is the word used to describe the material required to be turned over to the other side (when used as a noun). Both the prosecutor and the defense are required to turn over materials to each other to avoid surprise at trial, and this process is called "Discovery" (when used as a verb).
There are significant and dramatic consequences that can follow from a failure to turn over discovery. Prosecutors who have hidden discovery from defense lawyers have been sanctioned in court, had their cases dismissed, and, in extreme cases, been disbarred and even criminally prosecuted. Your lawyer should monitor the evidence carefully to make sure that the government has turned over everything they are required to.