a famous actor appearing with another famous actor in a film or a play, when both have parts of equal importance

The co-stars of "Casablanca" are Ingrid Bergman and Humphrey Bogart. 《卡萨布兰卡》由英格丽‧褒曼和汉弗莱‧博加特联袂主演。

to appear in a film or a play as a co-star

Katharine Hepburn co-starred with Spencer Tracy in many films. 凯瑟琳‧赫本和斯潘塞‧特雷西联袂主演了多部影片。