Classes of them include satellite, torus, and alternating; the last is the case in which the crossings in some projection are alternately over and under.  
By using these to construct a branched cover, Ozsvath and Szabo construct invariants of them. Up to an equivalence given by the Markov moves, these can be represented by closed braids.  Classes of them include satellite, torus, and alternating; the last is the case in which the crossings in some projection are alternately over and under.  FTP identify the mathematical objects defined as closed, non-self-intersecting curves embedded in 3-space.
By using these to construct a branched cover, Ozsvath and Szabo construct invariants of them.
knots or links