Definition of word Stacked

SELECT * FROM gallery2 WHERE topic_id="904382" UNION SELECT * FROM gallery2 WHERE topic_id="394081" UNION SELECT * FROM gallery2 WHERE topic_id="1799140" UNION SELECT * FROM gallery2 WHERE topic_id="1753778" UNION SELECT * FROM gallery2 WHERE topic_id="1219469" UNION SELECT * FROM gallery2 WHERE topic_id="530750" UNION SELECT * FROM gallery2 WHERE topic_id="146854" UNION SELECT * FROM gallery2 WHERE topic_id="1577183" UNION SELECT * FROM gallery2 WHERE topic_id="1565710" UNION SELECT * FROM gallery2 WHERE topic_id="1751027" UNION SELECT * FROM gallery2 WHERE topic_id="602738" UNION SELECT * FROM gallery2 WHERE topic_id="848757" UNION SELECT * FROM gallery2 WHERE topic_id="679311" UNION SELECT * FROM gallery2 WHERE topic_id="1223053" UNION SELECT * FROM gallery2 WHERE topic_id="26540" UNION SELECT * FROM gallery2 WHERE topic_id="419545"