What does "up to something" mean?
Native speaker’s answer
Rebecca
To be "up to something" is an informal expression meaning doing something secretly (usually meaning to be "up to no good"). When Taylor Swift sings "them boys up to something," she means that they are doing something secretly. Ex: The house is too quiet. I bet my kids are up to something. Ex: My enemy must be up to something. She hasn't bothered me in a while.