Meaning of prefix p,p′-?
I am guessing that this is the compound you are interested in:

Sigma labels this compound as p-Terphenyl-4,4′′-dicarboxylic acid (or 1,4-Bis(4-carboxyphenyl)benzene).

In your case, the p,p' indicates that the 2 carboxylic acids are in the para positions on 2 of the phenyl rings.