Clay animation or Plasticine animation  (Often called claymation, which, however, is a trademarked name).
klˈeɪ ˌænɪmˈeɪʃən ɔːɹ plˈæstɪsˌiːn ˌænɪmˈeɪʃən ˈɔfən kˈɔːld kleɪmˈeɪʃən, wˈɪtʃ, haʊˈɛvɚ, ɪz ɐ tɹˈeɪdmɑːɹkt nˈeɪm.