What is a "limited warranty"?

This mostly applies to SSDs, both internal and external. A limited warranty means that the warranty duration is a certain number of years OR until a certain threshold has been reached, whichever comes first.

In the case of SSDs, it is the TBW (Terabytes Written) count. The TBW (or any other limitations) will be specified on the product page. SSDs are designed for certain workloads, with consumer drives being budget oriented with a lower threshold. On the other end of the spectrum you get enterprise drives have the highest threshold - but also the highest price.

With a 3 Year Limited Warranty on an SSD that has a designed workload of 90 TBW, the warranty runs for three years or 90 TB written, whichever comes first.