Anni-Frid Synni Lyngstad KVO1kl (born 15 November 1945 in Bjørkåsen, Ballangen Municipality, Norway), also known simply as Frida, is a Norwegian and Swedish singer who is best known as one of the founding members and lead singers of the pop band ABBA. Courtesy titles Princess Reuss and Countess of Plauen are also in use because of her third marriage. Born in Bjørkåsen (in Ballangen Municipality), Norway, to a Norwegian mother and a German father, she grew up in Torshälla, Sweden, and started her first solo career there, as a jazz singer in 1967, through a talent competition called New Faces.

She won the competition with her song "En ledig dag", leading to a television appearance on Hylands Hörna on Dagen H; as a result, she was signed by EMI, and in turn was signed by Stig Anderson's record label, Polar Music, after years of releasing several singles and an album, Frida, under the earlier record label. She then had moderate success in Sweden, as she was a contestant for Melodifestivalen 1969 with her song "Härlig är vår jord". Lyngstad did not find international fame, however, until she joined ABBA, who have sold over 150 million albums and singles worldwide, making the group, which included her second husband Benny Andersson, one of the best-selling music acts in history.

After the break-up of ABBA, she continued an international solo singing career with mixed success, releasing the albums Something's Going On (1982) and Shine (1984); the latter being her last international album. In 1996, Lyngstad recorded her final album in Swedish, Djupa andetag (Deep Breaths), released by Anderson Records, before retiring from music.