Symbiosis is living together in a mutually beneficial and interdependent fashion. It is a complex interaction between plants, and between plants and animals. A total symbiotic cannot survive and propagate naturally without it's partner, and that partner does not mean a male/female relationship, but is frequently totally different. Symbiosis is crucial in the rainforest.
A good example of symbiosis in the rainforest is the ficus tree. It has flowers that only one type of wasp can pollinate. The insect has the right shape head and tongue to collect nectar for food, but also to pollinate the tree. Without the wasp, no fruit will ever be produced. The wasp gets essential nutrients, the flower gets pollinated. Now the fruit forms and protrudes up on the ends of branches. It is round and full of not only nutrients, but waxy coated seeds that cannot grow, the wax prevents the absorption of water. The fruit gets eaten by a leaf-nosed fruit bat that requires specific vitamins only provided by the ficus. The fruit passes through the bat and comes out as feces. The seed has been spread, fertilised and scarified, had the wax removed, so can now grow. The Wasps, trees and bats are all dependent on each other, and none could survive without the other.
There are also more generalized forms of symbiosis found in the rainforest. That ficus tree may shelter specific birds and insects that are essential to other organisms. It may also provide shade for smaller plants as well as trap moisture. Some of these relationships are not as clearly defined as the example given. Some plant may just double the odds of survival, but many creatures and plants sit on the edge of extinction and that slight edge is all that saves them.
Some researchers claim that as much as 80% of the rainforest is symbiotic with something else, when those symbiotic relationships is lost, so is the rainforest! Since there are over an estimated 10 million species found in the rainforests, 80% means that 4 out of 5 creatures and plants would disappear without symbiosis, and that translates into millions of species vanishing.
Symbiosis is living and working together in a mutually beneficial fashion and being co-dependent. It occurs through out the planet and is the way much of nature developed. It is what the rainforest is all about and crucial that people realize its importance. It is what life is about in general!