Starting from a special PainlevéBacklund transformation and a multilinear variable separation approach, the (2+1)dimensional generalized BorerKaup(GBK) system was analyzed,and a general variable separation excitation with some arbitrary functions for the (2+1)dimensional GBK system was derived.Based on the derived variable separation excitation and by selecting the arbitrary functions in the exact solution appropriately, such as certain localized functions and multivalued functions, a new type of solitary wave, i.e., a semifolded localized structure with practical meaning like ocean surface waves for the GBK system was constructed, and its evolution property of the novel localized structures was briefly discussed. The results show that it is completely elastic interaction,because the semifolded localized coherent structures are completely preserved,and their initial velocities, wave shapes and amplitudes are preserved after collision.