Concise Bible Dictionary:
Ceremonial uncleanness had a large place in the Jewish ritual (Lev. 5:3). It demanded separation from the camp for a time, and in many cases an offering must be brought before there could be restoration. It is typical of the moral uncleanness that separates from communion with God and the assembly.
Strong’s Dictionary of Greek Words:
Meaning:
from 3392; (morally) contamination (properly, the act)