shochuumimai
Shochuumimai (or shochuu o-mimai) are postcards that people in Japan send to friends during midsummer. They typically contain the phrase "暑中(お)見舞い申し上げます" (shochuu (o-)mimai moushi agemasu), which means something like "seeing how you're doing this midsummer".
See also
- zanshomimai (late summer)
- kanchuumimai (mid winter)