The Master Sword

The Master sword is typically the most powerful weapon in a Zelda game for general usage. The master sword will usually have a power level of two or three unlike the starting sword.

Ocarina of Time:
This legendary blade resides in the Temple of Time. Before Link can get it, he must collect all the three Spiritual Stones, and get the Ocarina of Time. This sword acts as a kind of key which allows Link to travel through time and is said to repel all evil.

A Link To The Past:
The legendary blade that rests in the Lost Woods of northwestern Hyrule in a pedestal with ancient Hylian inscribed on it, which says the hero with all three Pendants will weild it on cataclysm's eve. This blade has the power to emit a beam from its blade to attack enemies from a distance and has a power level of two. The Master Sword is also called "the blade of evil's bane", and has the power to repel evil magic.

http://www.zeldauniverse.net/images/stories/games/z10/items/mastersword.png

The Wind Waker
This version of the Blade of Evil's Bane, rests in a hidden chamber in Hyrule Castle, deep beneath the waves of the Great Sea. This Master Sword is also a kind of key, but this one is keeping the evil locked in time. When a young Link foolishly draws the blade, he awakens Ganon´s army from their ancient slumber. Later Link Learns that the Master Sword (After many years of being under the Great Sea) has lost its power to repel evil and Link must awaken two sages in order to regain that power.