I'm not an expert. However, "slate" is the name given to a list of candidates when your nominating source, typically Member of Congress or Senator, chooses to provide a SA with multiple names for the slot or slots which may be available. There are different types of slates: (i) “Principal Nominee with Competitive Alternates”, (ii) “Principal Nominee with Ranked Alternates”, and (iii) "Competitive Slate". All the gory details may be found in the stickies for the Nominations forum, here: