וַיִּוָּֽתְרוּ֙ בִּבְנֵ֣י יִשְׂרָאֵ֔ל אֲשֶׁ֥ר לֹֽא־חָלְק֖וּ אֶת־נַֽחֲלָתָ֑ם שִׁבְעָ֖ה שְׁבָטִֽים׃
And there remained among the children of Israel seven tribes, which had not yet received their inheritance.
Read midrashic interpretation of Joshua 18:2: and classical rabbinic exegesis.