Synthesis refers to the output of the task. For eg. if you take chemical substances, the reaction of chemical substances refers to “Synthesis”.
Synthesis in terms of post-reading, the word refers to one of the phase in the reading process where the content which is read are to be connected to what we know already and what we learnt newly. It is the outcome of reading.
There is one another term called “stimulation” which refers to the overall design of the reading.