Some constructions related to the homotopy groups include:

**Relative homotopy groups**: \({\pi_{n}\left(X,A,x_{0}\right)}\) is defined to be all homotopy classes of maps \({\left(D^{n},\partial D^{n},s_{0}\right)\rightarrow\left(X,A,x_{0}\right)}\) where \({s_{0}\in S^{n-1}}\) and \({A\subset X}\)**Stable homotopy group**: \({\pi_{i}^{s}\left(X\right)}\) is defined to be the group that the sequence \({\pi_{i}\left(X\right)\rightarrow\pi_{i+1}\left(SX\right)\rightarrow\pi_{i+2}\left(S^{2}X\right)\rightarrow\dotsb}\) eventually arrives at, recalling the suspension \({SX}\); a major unsolved problem in algebraic topology is computing the stable homotopy groups of the spheres*n***-connected space**: indicates that \({\pi_{i}=0}\) for \({i\leq n}\); so \({0}\)-connected = path-connected, \({1}\)-connected = simply connected**Action of \({\pi_{1}}\) on \({\pi_{n}}\)**: the homomorphism \({\pi_{1}\rightarrow\textrm{Aut}\left(\pi_{n}\right)}\) defined by taking the basepoint of \({\pi_{n}}\) around the loop defined by each element of \({\pi_{1}}\)*n***-simple space**: indicates trivial action of \({\pi_{1}}\) on \({\pi_{n}}\); a**simple**(AKA abelian) space is \({n}\)-simple for all \({n\Rightarrow\pi_{1}}\) is abelian**Eilenberg-MacLane space**: a space \({K\left(G,n\right)}\) constructed to have one nontrivial \({\pi_{n}=G}\), a rare case of \({\pi_{i}}\) uniquely determining the homotopy type; for any connected cell complex \({X}\), one can construct a \({K\left(G,n\right)}\) such that the homotopy classes of maps from \({X}\) to \({K\left(G,n\right)}\) are isomorphic to \({H^{n}\left(X;G\right)}\), thus turning homology groups into homotopy groups