Mouthplate

Instead of regular human facial features, some Transformers have what looks like a plate affixed to their lower jaw, usually covering up to their nose. While no official name exists for these, they are usually called 'mouthplates ' or 'faceplates ' (despite a 'regular' face once being described as a faceplate in the TV series). Two of the most famous examples are those of Generation One's Soundwave and Optimus Prime.

In earlier series, a Transformer's mouthplate moved when they spoke, as if there were a working jaw underneath. In Robots in Disguise and the Unicron Trilogy, however, it remains static.

Trivia

• Fan commentator Zobovor nicknamed these distinctive items "woobers" (crediting the term to a younger relative), and the name became popular with some fans.

• Some Optimus Prime toys have working mouthplates.
  
  
  From Teletraan I: The Transformers Wiki, a Wikia wiki.