From Longman Dictionary of Contemporary Englishsing along phrasal verbSINGto sing with someone else who is already singingSing along if you know the words. toJess was singing along to the radio. →sing→ See Verb table
Examples from the Corpus
sing to• I like things in the car to sing along to.• He sings along to a recordedguitarbackground.• I like songs that you can sing along to, and you can remember.• I was singing along to the Corrs quite happily when I noticed a group of people looking in my direction.• Jackie was singing along to the radio and didn't hear the doorbell.• You can also sing along to the songs if you wish.