Definition of duck face in US English:

duck face

noun

informal
  • An exaggerated pouting expression in which the lips are thrust outward, typically made by a person posing for a photograph.

    ‘the pop star pursed her lips into a duck face in one shot’
    as modifier ‘her duck face selfies’
    • ‘Don't make that stupid duck face in your photos.’
    • ‘Her smile is beautiful and I prefer it much more to that "duck face" she normally does.’
    • ‘Selfie after selfie, I scroll past the endless abyss of duck faces and over-filtered images tagged #nofilter.’
    • ‘Am I making too much of a duck face in this profile pic?’
    • ‘I signed up so that I can post selfies and duck face shots daily.’
    • ‘My daughter told me about "duck face" selfies, which are apparently a sub-class of the normal selfie.’
    • ‘I think she looks fine except for the duck face!’
    • ‘Daniel posted their selfie on Instagram, complete with duck face.’
    • ‘We'd complain about the pout, but this is one of the rare pictures where we think a duck face is not only appropriate, but necessary.’