Describes a state, condition, result, or relationship that is positive and without problems. Often used in formal, business, or medical contexts.
The test results were good.
Relations between the two countries are favorable.
The recovery after the surgery is going well.
My relationship with him is good.
According to the test results, his health condition was good.
Visibility is good today, and you can see the mountains far away.
良好 is a common formal word meaning 'favorable' or 'in good condition', used in reports and results, while 佳 is a more archaic, literary term for beauty or excellence.
良好 simply means 'in good condition' and is used for grades, results, or health checks, while 健全 implies a deeper, structural soundness rather than just a good state.
良好 means 'good, favorable' and is the formal opposite of 芳しくない, which means 'poor, unsatisfactory'.