We find that the Torah uses the word eidah (congregation) to refer to a group of ten people. Ten is the smallest group about whom such a term is used.
Moshe sent 12 spies to scout out the Land of Israel. Ten of the spies returned with an evil report. The verse refers to these 10 as an "evil congregation." We know this refers to only 10 of the 12, because two of the spies, Calev and Joshua, were righteous and gave a good report about the Land.