What does retract means in the science way?

Answer 1

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