It represents a commitment from the producer to you as a consumer on the durability of a good. More specifically, it is a commitment that the good will maintain its required functions and performance through normal use for the number of years indicated on the label. Otherwise, the producer must repair or replace the good at no cost. The producer has to describe the exact terms in the commercial guarantee statement.
As a consumer in the EU you also benefit from legal guarantee rights against the seller. The legal guarantee applies independently of any commercial guarantee.