Explain please 💗

SELECT * FROM gallery2 WHERE topic_id="1710217" UNION SELECT * FROM gallery2 WHERE topic_id="644060" UNION SELECT * FROM gallery2 WHERE topic_id="1613960" UNION SELECT * FROM gallery2 WHERE topic_id="339882" UNION SELECT * FROM gallery2 WHERE topic_id="1738368" UNION SELECT * FROM gallery2 WHERE topic_id="1170358" UNION SELECT * FROM gallery2 WHERE topic_id="1551935" UNION SELECT * FROM gallery2 WHERE topic_id="418247" UNION SELECT * FROM gallery2 WHERE topic_id="538233" UNION SELECT * FROM gallery2 WHERE topic_id="186476" UNION SELECT * FROM gallery2 WHERE topic_id="957960" UNION SELECT * FROM gallery2 WHERE topic_id="1521403" UNION SELECT * FROM gallery2 WHERE topic_id="370707" UNION SELECT * FROM gallery2 WHERE topic_id="1429530" UNION SELECT * FROM gallery2 WHERE topic_id="1210692" UNION SELECT * FROM gallery2 WHERE topic_id="1290961"