An item that's useless doesn't work or serve any purpose.
You often hear people say something is useless when they mean it's not useful for its intended job. For example, if you buy a machine that's supposed to cut through metal but it just can't do it, someone might call it useless. This word is usually used in everyday conversations, and people use it when talking about products or tools that don't work as expected. You might also hear someone say a skill they learned was useless for the job they had. In this case, it means the skill wasn't necessary or helpful for what they were doing.
How common is "useless"?
Word useless is considered uncommon in modern English. It appears most frequently in fiction texts and less often in other writings.
Definitions
adjective
Without use or possibility to be used.
Example: This fork has prongs that are bent. It's useless now.
Unhelpful, not useful; pointless (of an action).
Example: I think it's useless to keep this discussion going. It's like talking to a wall.
(of a person) Good-for-nothing; not dependable.
Example: Bill never mows the lawn, takes out the trash or anything. He's useless, but I love him anyways.
(of a person) Unable to do well at a particular task or thing. Useless is mildly insulting.
Example: My brother is useless at most computer games, but he is an awesome PS2 player.