In athletic contests or activities, there are several titles for the people getting different places. The person who get the top place is called "冠军 (guàn jūn, champion)", followed by "亚军 (yà jūn, runner-up)" and "季军 (jì jūn, second runner-up)".
Speaking of it, the word "冠军 (guàn jūn)" has long been used since the ancient time in China. Far back in 209 BC, there was a general from Chu called "宋义 (sòng yì)", who rose up against the tyrannical rule of the Qin Dynasty. Song was so brave and skilful in battle that he defeated soldiers of Qin again and again. The soldiers of Chu awarded him with the title "卿子冠军 (qīng zǐ guàn jūn)" for his remarkable battle achievements. He was the first person that had won the title "冠军 (guàn jūn)" in Chinese history.
"冠军 (guàn jūn)" was still in use in the Han Dynasty. Since Han, "冠军 (guàn jūn)" has been used as an official title of the military generals with remarkable battle achievements. In the Qing Dynasty, the head of imperial guard that protected the emperor was called "冠军使 (guàn jūn shǐ)".
As "亚 (yà)" means "second-class" in Chinese, "亚军 (yà jūn)" refers to the runner-up who is inferior to the "冠军 (guàn jūn)". In ancient times, scholars called Confucius "至圣 (zhì shèng)" and Mencius "亚圣 (yà shèng)".
As for "季军 (jì jūn)", it means the second runner-up who gets the third place following "冠军 (guàn jūn)" and "亚军 (yà jūn)". In the old Chinese calendar, the three months in spring season were separately named "孟春 (mèng chūn)", "仲春 (zhòng chūn)" and "季春 (jì chūn)". Three brothers in a family were ranked as "伯 (bó, the eldest brother)", "仲 (zhòng, the younger brother)" and "季 (jì, the youngest brother)" based on their ages. "季 (jì)" in these two examples means "the third".
Now the words "冠军 (guàn jūn)", "亚军 (yà jūn)" and "季军 (jì jūn)" are all used to address the people who win awards in activities like athletic contests or entertainments.
Please visit Chinlingo for Chinese learning.