Shallow: of little depth
Mildred is indirectly characterized as ignorant in "Fahrenheit 451". One example of this is how she stays home all day watching TV and listening to her music. Another thing that describes her as ignorant is that she doesn't speak with Montag at home and she doesn't care about Clarisse's death. This is a indirect characterization because it doesn't explicitly tell us about Mildred, but we can gather this information based on the events in the story.
Mildred was directly characterized as stupid. One example is when she snatches the phone and said "the white clown's on tonight'. Then Montag steps in the kitchen, throws the book and says, "you are really stupid." This is an example of direct characterization because the words are explicitly spoken; the audience does not have to gather clues to support the information either.