Obsolescence means a piece of technology is no longer fit for purpose. It may be too slow, no longer precise enough, or otherwise no longer economical to use: people often do not have stuff repaired, for the simple reason it is more expensive than buying a new and more modern item.
There are also those who feel the manufacturers are pushing obsolescence down the customer's throats, by making sure products only work for slightly longer than the period of warranty. But economy has always been a circular thing: there are those who buy new products, and those who prefer to buy secondhand products.