Answer:
Trochaic Octameter.
Step-by-step explanation:
Trochaic octameter is the poetic foot of a line in poetry where there are eight feet/ syllables per line. The foot of each word has two syllables where a stressed syllable is followed by an unstressed syllable.
In the given poetry of Edgar Allen Poe, the lines all contain stressed syllables followed by unstressed syllables, alternating between the two. This is evident in the first lines of the poem-
Once upon a midnight dreary,
while I pondered weak and weary,
The ones in bold signify the stressed syllables while the rest are the unstressed syllables.