Back in 1970 my friends and I were chatting with our favorite teacher about music. There was a short, curious little song by Tin Tin called, "Toast and Marmalade for Tea".
The song was only verse, repeated - there was no chorus!
The teacher laughed and said, "that song is a key". In the past there were lots of short songs that had no chorus, and if they were three minutes or less, those songs were refered to as "keys".
More than 50 years and I'm still wondering, if "Toast and Marmalade for Tea" is a musical key - where is the lock?