Recessions and unemployment are trouble enough, but many people in the modern world see a danger in too much prosperity. The danger is inflation.
Inflation is defined as an increase in the average price level in the economy.
Thus, we express the overall price level by a price index, that is, an average of these different rising and falling prices. But a simple average won't do. Some prices are more important than others. Instead we use a weighted average with weights that reflect the importance of the different products in production. Since a lot more computers are produced than buggy-whips, we would give computers a heavier weight.