Any member of the eukaryotic group of organisms, which also includes the more well-known mushrooms and microbes like yeast and mold, is referred to as a fungus.
Fungi can be saprophytic (feeding on dead plant and animal matter), parasitic (feeding on a living host), or symbiotic (feeding on both) (they share a mutually beneficial relationship with another organism).
Endothia parasitica, Ceratocystis ulmi, Puccinia sparganioides, Puccinia graminis are parasites of plants, while fungi of the genus Aspergillus or Candida albicans carry infections to human organisms.