Tempo has to do with the relative rapidity, basically the overall speed of the golf swing. When you look at great tour players, Nick Price has a faster tempo than Ernie Els.
Rhythm is the movement with uniform or patterned recurrence, basically the relative duration of each of the swing parts. Generally, the backswing is slower than the downswing. For good golfers, you'll usually see a 2:1 rhythm, which means the backswing takes twice as long as the downswing.
The most important part of the golf swing happens when rhythm and tempo come together - the transition to the downswing. When you've got the right tempo, the downswing will flow into the ball with easy power. Tempo and rhythm affect every shot you hit. If you want to have a great swing, you've got to have the right golf swing tempo, golf rhythm, and golf transition from top.
Tempo varies from golfer to golfer, so it is really about finding the right one for you. let's go back to the example of Nick Price and Ernie Els. Price is quick guy. The way he walks, the way he talks, all lead to a faster golf tempo. Els is a laid back kind of guy and his tempo reflects it. Both have different tempos, but the flow of power to the club head is uninterrupted for both players.. When they're making the cut and find themselves in pressure situations, their individual tempo is what they continue to come back to to be their own comfort zones.
Your golf tempo may not be like Price's or Els', but when you find it, and pair it with your golf rhythm, you'll find the golf transition from top to downswing will be much more fluid, dependable and consistent. Check out these golf aids that will make your golf training more productive and consistent.