What is a garden weed?

Excuse me, but could you please clarify what exactly is meant by the term "garden weed"? I understand that it refers to some sort of plant that is considered undesirable in a garden setting, but what specific characteristics or traits define a weed in this context? Is it simply a matter of aesthetics, or are there other factors at play, such as the weed's potential to harm other plants or compete for resources? I'm interested in learning more about how gardeners identify and manage these types of plants.