Arete (ἀρετή) - excellence of any kind
It is a fulfillment of purpose, or potential. In Homer's writings, it meant effectiveness.
"Men and women who used all of their faculties - strength, bravery and wit - to achieve real results." (Wikipedia)
As you apply the concept to different areas of live, it expands and grows to accommodate the breadth of human excellence.
Physically, it has meant athleticism. Exercise as an education on the body and its possibilities.
The "verse" cleanliness is next to godliness comes to mind. The attention to detail that a thorough cleaning takes. The fact that cleaning means returning something to its best state, which means acquiring some knowledge of that thing.
Mentally, it means purposeful study. "Virtue is knowledge" and "Arete is knowledge".
Most importantly, arete requires being excellent at the right things. It means finding the most effective use of your talents. The most beautiful use. Being excellent at the wrong things betrays a lack of excellence in self-awareness.
Arete for a horse is different than for a tree.
Arete for a singer is different than for a barista.
Arete for a healthy human may be different than for a good citizen.
True excellence is never arbitrary. We don't have the luxury of just getting better at what we are already good at. Or what is habitual. To be meaningful, it must be a challenge, a suffering consciously undertaken.
I'll end with a quote from a great book that I would recommend to anyone who might be achieving excellence at the wrong things instead of arete.
"Because the brain mediates our experience of the world, any neurosurgical problem forces a patient and family, ideally with a doctor as a guide, to answer this question: What makes life meaningful enough to go on living?
I was compelled by neurosurgery, with its unforgiving call to perfection; like the ancient Greek concept of arete, I thought, virtue required moral, emotional, mental, and physical excellence. Neurosurgery seemed to present the most challenging and direct confrontation with meaning, identity and death."
-Paul Kalanithi, When Breathe Becomes Air