From WordNet (r) 1.6 [wn]:

  synthesis
       n 1: the process of producing a chemical compound (usually by the
            union of simpler chemical compounds)
       2: the combination of ideas into a complex whole [syn: {synthetic
          thinking}] [ant: {analysis}]
       3: reasoning from the general to the particular (or from cause
          to effect) [syn: {deduction}, {deductive reasoning}]

Synthesis is the part that matters in human information processing and knowledge acquisition. It is the moment when the observed or the apprehended becomes known and we can use that gain for future insight.