an example of a parasitic relationship, involving a fungus, is bread with breadmold (molds are fungi)
parasitic relationships are unfair and one sided - the parasite feeds off the host, and the host's energy/nutrients/water supply are drained. the relationship eventually comes to an end once the fungus has completely sucked the water and nutrients out of the host, or disintegrated it into nothing, or the fungus is killed or taken off/out of the host.