At the end of Edgar Allan Poe's "The Fall of the House of Usher," eponymous house, in which the Usher family has lived for generations, dramatically collapses. This fall is the literal meaning of the story's title. But the story's title has another meaning, a metaphorical meaning, that is of equal or greater importance.

One can refer to a noble family as being a "house." This is an example of metonymy, a figure of speech in which one thing is understood in terms of another kind of thing due to association or proximity. Metonymy is related to metaphor, but the two figures of speech differ in the kinds of connection they trace. Put concretely, a family is not like a house; rather, a family lives in a house.

In “The Fall of the House of Usher,” readers encounter a noble family that has been in decline from its former glory for quite some time. In the dramatic deaths of Roderick and his sister Madeline, the family is entirely extinguished, because Roderick and Madeline are the last two members of the House of Usher. This fall is the figurative meaning of the title.

The deaths of the Usher siblings is also literal fall in that Roderick and Madeline collapse to the ground together. At this stage of the story, the literal and figurative meanings of the title coalesce, perfectly illustrating its multiple meaning.

In "The Fall of the House of Usher," what is meant by the “fall” of the house of Usher, both literally and symbolically?

You have picked up on a very important aspect of the title. Of course, the "fall" in question works on many levels that are key to the story and the brooding atmosphere of evil that Poe creates through setting and character. There seems to be a real, supernatural kind of relationship between the literal House of Usher as in the location, and its two surviving members, the stricken Madeline and Roderick.

You will want to think about how in the description of the narrator's first sight of the house it is clear that it is given a supernatural menace:

The discolouration of ages had been great. Minute fungi overspread the whole exterior, hanging in a fine tangled web-work from the eaves... In this there was much that reminded me of the specious totality of old woodwork which has rotted for long years in some neglected vault, with no disturbance from the breath of the external air.

Note the important emphasis that is placed on the rot and decay - a rot and decay that is symbolically present in the line of the heirs of the Usher family too, as we discover, for both Roderick and his sister Madeline suffer from a mysterious ailment that has changed them both dramatically. Consider how Roderick is described:

A cadaverousness of complexion; an eye large, liquid, and luminous beyond comparison, lips somewhat thin and very pallid, but of a surpassingly beautiful curve; a nose of delicate Hebrew model, but with a breadth of nostril unusual in similar formations; a finely moulded chin, speaking, in its want of prominence, of a want of moral energy; hair of a...