Select the most appropriate meaning of the given idiom.

At the drop of a dime

Something that can happen very fast without hesitation

The most appropriate meaning of the idiom "at the drop of a dime" is (3) Something that can happen very fast without hesitation.

The other options do not fit the meaning of the idiom.

• A way of saying that you are happy to see someone is "I'm glad to see you."
• Something that is not popular is "a niche market."
• Extremely easy to understand is "a no-brainer."

The idiom "at the drop of a dime" is used to describe something that can happen very quickly and without any thought or planning. It is often used to describe someone who is very willing to help or to do something, as in "I'll be there at the drop of a dime."