AFAIK:
usualy when you are making a compound, you do it like this:
A + B
X then testing for biological activity then you make another one with different structure..
A + C
Y etc..
and you are required to do purifications etc..
for biological activity
In Solution-Phase Parallel Synthesis you do it like this:
A + B + C+...
X+Y+...
So you have a mixture of compounds in one batch and then you can do the screening with all at once after you get rid of unreacted reactants. SO you do the screening and results are negative: ok i dont continue with those 10 compoudns, its positive: you separate and figure out which one it was