Rewards allow a player to gain extra ships or cards. In an encounter, defensive allies can claim rewards if the defense wins the encounter. Each defensive ally can draw one card from the deck or retrieve one ship from the warp for each ship the player sent to help defend. If playing with Cosmic Incursion or Cosmic Dominion, a player may draw cards from the reward deck if the player chooses to draw cards for rewards.
The Fantasy Flight Games edition of Cosmic Encounter sometimes refers to rewards as "defender rewards" or "defensive ally rewards." These terms all mean the same thing and the use of them is likely an oversight on FFG's part.