drop-in
/ˈdrɒpɪn/adjective
1
- visited on an informal basis without booking or appointments顺便（或偶尔）去一下的, 无须预约的：
a drop-in disco.
一家无须预约的迪斯科舞厅。
2
- (of an object such as a chair seat) designed to drop into position（座椅等）嵌入式的。