Midsummer/ˌmɪdˈsʌmər/ Definition 1 of 3Pro Tip 1/3Specific Timing Midsummer refers to a specific point in summer, often celebrated as a day. Let's plan our family reunion for midsummer. Pro Tip 2/3Cultural Celebrations Many cultures have unique customs and festivities for midsummer. They light bonfires on midsummer as a local tradition. Pro Tip 3/3Seasonal Change Midsummer marks when days start shortening as the season progresses. After midsummer, the nights gradually get longer.