A person in desperate circumstances or who is at the point of desperation, such as a down-and-outer, addict, etc.

In dire need of something.

“I hadn't eaten in two days and was desperate for food.”

Being filled with, or in a state of despair; hopeless.

“I was so desperate at one point, I even went to see a loan shark.”

Without regard to danger or safety; reckless; furious.

“a desperate effort”