What is the origin of the idiom "hot air" and when to use it?

The idiom "hot air" has its origin in the concept of heated or inflated air that lacks substance or significance. The phrase metaphorically refers to empty or exaggerated talk that lacks truth, substance, or value. It is used to imply that the speaker is engaging in idle chatter, making grandiose claims, or offering empty promises without any real substance or intention to follow through.