promenade concert
US /ˈprɑːm.ə.nɑːd ˌkɑːn.sɜːrt/
UK /ˈprɑːm.ə.nɑːd ˌkɑːn.sɜːrt/

1.
a concert of classical music at which part of the audience stands rather than sits
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We attended a wonderful promenade concert in the park last summer.
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The BBC Proms are a famous series of promenade concerts held annually in London.