Concise Bible Dictionary:

The hill of Ares, or Mars. Here was held the highest and most ancient and venerable court of justice in Athens for moral and political matters. It was composed of those who had held the office of Archon unless expelled for misconduct. Paul, who had been disputing daily in the market place, was conducted by some of the Epicurean and Stoic philosophers to Mars’ Hill, not for any judicial purpose, but doubtless that they might hear him more quietly. Here he delivered his address respecting God, so suited to the heathen philosophers who heard him, and which was not without its fruit (Acts 17:1919And they took him, and brought him unto Areopagus, saying, May we know what this new doctrine, whereof thou speakest, is? (Acts 17:19)). The Greek words are Areios-pagos, but are translated Mars’ Hill in Acts 17:2222Then Paul stood in the midst of Mars' hill, and said, Ye men of Athens, I perceive that in all things ye are too superstitious. (Acts 17:22). The court was situated on a rocky hill opposite the west end of the Acropolis. Sixteen stone steps still lead up to the spot.
Mars’ Hill

Strong’s Dictionary of Greek Words:

probably of foreign origin; a hillock
KJV Usage: