Answer: Trash represents connotative meaning of a person who is low-class or worthless.
The connotative meaning of a word is an association that the word carries besides its literal meaning (denotation). In this case, the denotative meaning of "trash" is that of garbage, rubbish, or other things that need to be discarded. However, the connotative meaning of the word is that of a person who belongs to a low class. This is the meaning Aunt Alexandra refers to when she calls people "trash" because of the way they are dressed.