General: To pull back inside (for example, an airplane
retracting its wheels while flying); To take back or withdraw
something one has said
Mathematics:
1. In category theory, a branch of mathematics, a section is a
right inverse of a morphism. Dually, a retraction is a left
inverse. In other words, if and are morphisms whose composition is
the identity morphism on Y, then g is a section of f, and f is a
retraction of g.
2. In mathematics, in the field of group theory, a subgroup of a
group is termed a retract if there is an endomorphism of the group
that maps surjectively to the subgroup and is identity on the
subgroup. In symbols, is a retract of if and only if there is an
endomorphism such that for all and for all
Topology:
In topology, a retraction, as the name suggests, "retracts" an
entire space into a subspace. A deformation retraction is a map
which captures the idea of continuously shrinking a space into a
subspace