Gyeongseong (경성; 京城) is the Korean form of Keijo (京城), the former Japanese name of Seoul used during the Japanese Occupation of Korea. Gyeong (경; 京) means "capital" and seong (성; 城) refers to Hanseong (한성; 漢城), the name of Seoul during the Joseon Dynasty. The name survives today in the names of various railway lines and freeways, including:
Gyeongui Line (Gyeonguiseon; 경의선) between Seoul and Dorasan (the ui comes from Sinuiju, the Revised Romanized spelling of Shinŭiju (신의주) in North Korea, the line's original terminus on the Chinese border--see the article on the Gyeongui Line for details);
Gyeongwon Line (Gyeongwonseon; 경원선) between Seoul and Shintanni (originally the line went to Wonsan (원산) in what is now North Korea); and
Gyeongchun Line (Gyeongchunseon; 경춘선) between Seoul and Chuncheon (춘천) in Gangwon Province.