'Foot' is how Biden introduces himself, initially? (4)

I believe the answer is:

iamb

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'foot' is the definition.
(type of metrical foot in poetry)

I can't explain the rest of the clue.

(Other definitions for iamb that I've seen before include "Line of verse" , "Short-long metrical foot" , "Short-long metric foot" , "Poet's foot" , "Part of a pentameter?" .)

I've seen this clue in The Guardian.

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