4/4 time is 4 beats or pulses per measure and each of the beats is the duration of a quarter note. Tempo is the speed at which this pulse takes place. A measure is a division of the pulse into groupings of 4 in the case of 4/4 time. Underlying all rhythm is a pulse which is like a heartbeat. Rhythm is usually a further division of the pulse into rhythmic figures and phrases.
4/4 time is typically accented on the 1 beat of each measure with a less strong accent on beat 3. Chord charts are most often written using measures and bar lines.
4/4 Em / / / | Am / / / | Em / / / | Am / / / |
The above is a 4 measure phrase or 4 “bars” long. When chords are written in this way it becomes easier to memorize progressions and song form. Songs are typically made up of 4 measure phrases which often when grouped become 32 measure or 16 measure or 12 measure forms.
When chord progressions are written without the use bar lines and chords are written only above the words this can cause a considerable amount of confusion when trying to understand and memorize the form of a song. The best chord charts separate the chords into bar lines and can even go so far as to include sections as Chorus, Verse, Bridge.