The invention discloses several types of fastener, fastening systems, fastener assemblies and related areas.In particular, the invention discloses a releasable fastening system (150) which has a pin (152) with a locking cavity (163). The pin is intended for insertion in an aperture (154). A locking means (158, 160) engages the locking cavity (163) of the pin (152) when the pin (152) is received in the aperture (154). The system (150) also includes unlocking means (162) which includes material adapted to contract when activated. When a material contracts, engagement means (158) included in the locking means (158, 160), disengage the locking cavity (154).