Rashi defines as having a machshava at the time of doing one of the 4 avodas - shechita, kabala, holacha, zerika - to intend to either feed people (meat) or the miz'beiach (eimurin/dam) after the appropriate time. The gemara says that when a korban becomes passul due to a thought of pigul, it is only considered pigul if it was completed properly without any other p'sul mixed in. But, if the korban would become invalid by something done later such as a machshava of lo lishma by chatas, or a machshava of the wrong place by all korbanos, it would retroactively remove the issur pigul. Meaning, that the more severe prohibition of pigul for which the punishment is kareis, only applies when the korban retains is kashrus in all other areas.
R. Yakov Kaminetzky (parshas kedoshim) conceptualizes this point. The more precious something is, and the holier that it is, the easier it is to defile because the impurity is more noticeable. It is for this reason that the Torah places greater demands on klal yisroel than the other nations, because any impurity will stand out. He points to the statement we make in selichos - Ashamnu mi'kol Am - we are guiltier that all other nations. That is certainly not true. But it means that since we are meant to be the showcase of behavior and represent Hashem on earth, any impurity stands out like an ugly stain on fine white material. Therefore, when a korban becomes passul for some other reason, it no longer retains its stature and retroactively isn't susceptible to becoming pigul.