1) It has eight feet 2) The Raven feature 3) Type of verse 4) Verse 5) Verse line 
Octameter in poetry is a line of eight metrical feet. It is not very common in English verse. E.g.: - Trochaic Iambic Dactylic ...
• (n.) A verse containing eight feet; as, --//Deep# in|to# the | dark#ness | peer#ing, | long# I | stood# there | wond`#ring, | fear#ing.
A verse containing eight feet. Algernon charles swinburne's 'march
Oc·tam'e·ter noun [ Confer L. octameter in eight feet. See Octa- , and meter .] (Pros.) A verse containing eight feet; as, -- « Deep\'b6 in - to\'b6 the - dark\'b6ness - peer\'b6ing, - long\'b6 I - stood\'b6 there - wond'\'b6ring, - fear\'b6ing.» 
Is a line of poetry containing eight metrical 'feet'. Octameter is the longest line included in the formal classification of lines. The Raven by Edgar Allan Poe is written in trochaic octameters.
[n] - a verse line having eight metrical feet
noun a verse line having eight metrical feet