The difference between symbiosis and parasitism lies in the nature of the relationships they describe. Symbiosis is a broad term that refers to any close interaction between two species, which can be beneficial, neutral, or harmful. In contrast, parasitism specifically involves one organism, the parasite, benefiting at the expense of another organism, the host, causing it harm. Therefore, while all parasitic relationships are symbiotic, not all symbiotic relationships are parasitic.