How do we understand and define the concepts of higher torsions in algebraic topology?
Foe example, I know that the torsion group is related to the finite group sector of cohomology group or cobordism group, etc.
Is the common torsion group called 1-torsion?
How do we define 2-torsion? Is that part of cohomology group of $B^2G$?
How do we define 3-torsion? Is that part of cohomology group of $B^3G$?