Simple meters versus compound grouping
The time signature tells you two things: the numerator is how many beats per measure, and the denominator is which note value gets the beat. In 4/4 (four-four), there are four beats per measure, and the quarter note gets one beat. This is the most common time signature in pop and rock because four beats feel natural and stable. 3/4 (three-four, waltz time) has three beats, creating a lilting, dance-like feel. 2/4 and 2/2 are less common but create a driving, marching quality.
The 'feel' of a time signature comes from grouping. Four beats group into two pairs (strong, weak, strong, weak). Three beats group as one group of three. This grouping shapes where accents land and how melodies phrase.
Odd meters and listener engagement
5/4 (five-four) is awkward at first because five beats do not group evenly. Some musicians count it as 3 + 2, others as 2 + 3. 5/4 creates a limping, unsettled feeling that composers and progressive bands use to suggest strangeness or intensity. 7/8 and 7/4 are similarly unusual. Jazz standards like Take Five popularized 5/4 enough that modern listeners accept it without thinking.
6/8 (six-eight) and 12/8 (twelve-eight) are compound meters where the beat itself divides in three. Six eighth notes per measure group as two beats of three eighth notes each, creating a lilting, rolling groove different from the straight-ahead feel of 6/4. Blues shuffles and folk music frequently use 12/8 for its natural swing. Mixing simple and compound meters within one song creates rhythmic interest.