open day

 Longman Dictionary of Contemporary English 5++朗文当代英语 5++LDOCE 5++朗文 5++ˈopen day noun [countable] British English  SSHOW/LET somebody SEE somethinga day when a school or an organization invites the public to come in and see the work that is done there 〔学校或机构允许公众参观的〕开放日，参观日

Examples from the Corpus

open day• Opening success: More than 1000 people visited Middlesbrough botanic centre's open day.• Members of the public took the opportunity to see for themselves in a unique open day.

ˈopen day nounChineseSyllable  

a or a Corpus an when day school

open day
ˈopen day noun [countable] British English
a day when a school or an organization invites the public to come in and see the work that is done there

open dayBrE /ˈəʊpən deɪ/ 🔊NAmE /ˈoʊpən deɪ/ 🔊 (BrE) (NAmE ˌopen ˈhouse) nouna day when people can visit a school, an organization, etc. and see the work that is done there （学校、机关等的）开放参观日，开放日