Fungus

A biological kingdom including yeasts, molds, and mushrooms. Distinctive features:

• Heterotrophy (no photosynthesis)
  
• Chitin in cell walls
  
• Movement via growth (though spores occasionally flagellated)
  

Molds and mushrooms are particular structural forms fungus can take.

Not fungi:

• Mosses: They're plants
  
• Algae: They're photosynthetic, though not plants
  
• Slime molds and water molds: Not actually molds. People used to consider them fungi, they're actually… Something Else
  

Lichens are symbiotic colonies of fungus and algae (“fungi that have discovered agriculture”¹).