September is National Chicken Month
Don't Know Much About Geography
Dream, dream, dream.
Cliches and the Truth They Contain
Themes come from holidays-real and manufactured-, nostalgia, motivational words, songs, TV shows and more.
Our club uses themes to help the Topic Master anchor his/her questions. But they're just a starting point and the Topic Master isn't bound to stick with the theme of the day.
I hope this is something of the kind of answer you sought.