What is a science definition symbiotic relationship?

A symbiotic relationship is one that is beneficial to both parties. Lichen is a common example.

Another relationship is parasitism, where one member extracts food from the other but offers nothing in return. Mistletoe plants are this category.

And a third relationship is epiphytic, where one member takes advantage of position, but takes nothing from the host. Lianes, and perching plants demonstrate this.