1.) A state of mind where one mourns the loss of the freedoms and/or temporary relationships of summer.

2.) This song is sung by Lana Del Rey
Scenario 1:

Girl (with her head against the window)

Friend: "what's the matter? You've been like this since September."

Girl: "I don't know... I guess I just have that summertime sadness."

Friend: "I know what you mean: I wasted mine, too, and I wish I could get it back."

Scenario 2:

I got that summertime,
Summertime sadness.
Summertime sadness.
I got that summertime,
Summertime sadness,
Oh, oh-oh-oh oh-h...
by The Quiz-Trivian-Naire October 21, 2013
A:Hi, I'm a Lil' Fucker
B:What's your favorite song?
A:Summertime Sadness Remix, perfection
B:Fuck you
by Lunudelflop August 31, 2020