  In this paper we propose the most general classification of point-like and
line-like extrinsic topological defects in (2+1)-dimensional Abelian
topological states. We first map generic extrinsic defects to boundary defects,
and then provide a classification of the latter. Based on this classification,
the most generic point defects can be understood as domain walls between
topologically distinct boundary regions. We show that topologically distinct
boundaries can themselves be classified by certain maximal subgroups of
mutually bosonic quasiparticles, called Lagrangian subgroups. We study the
topological properties of the point defects, including their quantum dimension,
localized zero modes, and projective braiding statistics.
