Yes, that's right! Every song has a key it's played in. So what does this mean? Well every key (note) on the piano has its own scale with 6 other notes in the scale. They are numbered from 1-7. So when you hear someone say a song is in the key of this or that it means the scale that is associated with that key are the notes used in the song. Whether it be in the form of chords, a melody, or the bass (your left hand), they all must work together to be in the same key.
Hope this helps someone! Any questions? Leave a comment.