What does negative energy imply?

I know energy comes in a number of forms and every form of energy is defined uniquely.

But if I had to give a broad definition of energy, I would define it as "ability of a system to perform work."

Using the above definition doesn't make any sense while trying to explain negative energy. So what does negative energy mean?

Answer

If positive work is "work done by the system" then negative work is just "work done on the system". The sign just tells if energy is added to the system or leaving the system.