What is a phrase? In music, a phrase is originally, literally, a breath. Much early music was vocal music and flute music, and people got in the habit of organizing music into chunks that could be sung or played in one breath.
That original idea of a phrase often holds true in more recent music, but not always. Some slow songs have long phrases that require a singer to catch an extra breath in the middle. And in some fast songs with non-stop lyrics, a singer might get through two phrases on a single breath.
In a rock song, a phrase is typically 4 or 8 bars long. But phrases can be just about any length; you'll see them as short as 2 bars, and as long as 16 bars.
A phrase makes a coherent musical point. If you were going to cut up an instrumental track into pieces and rearrange it in a different order, you'd have a fighting chance of making musical sense if you cut it up phrase by phrase. If you cut it up any other way, you'll just make a musical mess.
One of the important things drummers do is play fills or other gestures to help clarify where the phrases begin and end. Listen carefully to the drum track and take note of what the drummer is doing to give structure to the song.
Like so many things in music, it's hard to precisely define what qualifies a chunk of music to be called a phrase. But in most ordinary rock songs, the structure of phrases is perfectly clear and easy to hear, even when we can't exactly say why.
We'll talk more about phrases when we get into the structure of a song. But we need to talk about phrases now in connection with chords. Certain sequences of chords make a musically sensible phrase, while other sequences of chords just don't. We'll soon start to look at how to put chords together to make a phrase.