Time signature, often also referred to as ‘meter’ sets the groove of the song. The common as well the simplest one of all is the 4/4 timing. The first number or the numerator refers to how many counts or beats there are in one bar and the second number, the denominator refers to the duration of each count or each beat. Therefore a 4/4 time refers to 4 beats in each bar and each beat getting a duration of (1/4) quarter note.
On the same note, a 3/4 time refers to 3 beats per bar and each beat having a value equal to a quarter note. In simple terms, on 3/4 timing, there will be 3 counts in each bar. This time signature is commonly known as waltz time.
A 2/4 then will have 2 counts in each bar. This is often referred to as march time as this mimics the sound of marching (1-2.1-2.1-2…)
Now things get interesting if we change the denominator. For example if you take a 2/2, it says there are two beats per bar and each beat is equal to (1/2) half note. Now a half note has twice the value of a quarter note. So 2 half notes is basically the same as 4 quarter notes, so where is the difference between these two?
Technically, duration wise, there is no difference. But how we play this and how it feels altogether is certainly different. Let me put the 4/4 and 2/2 in tandem
4/4 1 2 3 4| 1 2 3 4
2/2 1 2 | 1 2
On 4/4, a musician is likely to tap the foot on all 4 beats, accenting the strum on all 4 beats where as in 2/2 there will only be two taps, two beats and therefore two accents. The bigger space between the accents in 2/2 creates more swing than it will have in 4/4. So even though the difference is very subtle, there is a difference indeed.