Synthesis is the co-dependant co-existing of two organisms. For example an ant and an aphis. Aphis provides food to the ants and ants provide safety for the aphis.

although, there are dozens more things that can be describes with the word synthesis, fe. read more on the wikipages

Total synthesis, the complete organic synthesis of complex organic compounds, usually without the aid of biological processes

Convergent synthesis or linear synthesis, a strategy to improve the efficiency of multi-step chemical syntheses

Dehydration synthesis, a chemical synthesis resulting in the loss of a water molecule

Paal-Knorr synthesis, a chemical reaction named after Carl Paal and Ludwig Knorr Biosynthesis, the creation of an organic compound in a living organism, usually aided by enzymes

Sound synthesis, various methods of sound generation in audio electronics

Wave field synthesis, a spatial audio rendering technique, characterized by creation of virtual acoustic environments