What is a "limited lifetime" warranty?

Limited lifetime warranties normally apply to RAM, and it means that the warranty covers the lifetime of the product (in other words, the warranty runs for as long as the item is in production). It is not a "forever" warranty, but normally lasts at least another two generations after a new product comes out. In other words and as an example, DDR2 carried a warranty until at least DDR4 was released, and DDR2 warranties were still being honoured after the launch of DDR5.