Forres: Forres is a castle in Scotland where Duncan lives. They are battling near his castle to ward off the Norwegian invaders. When Macbeth becomes king, he will live at Forres and Banquo will be murdered only a mile from the castle.
Prophecies: The witches' prophecy that Macbeth will become king of Scotland sets off Macbeth's murderous streak. The same prophecy named Banquo's descendants as the successors to the throne, and this made Banquo an enemy in Macbeth's eyes.
Banquo's Ghost: Banquo's ghost is a manifestation of Macbeth's guilty conscience. The ghost appears at a banquet at the Forres castle, and when Macbeth sees the ghost, it stirs suspicion in the thanes.
Second Vision: The second vision tells Macbeth that no one of woman born will kill him. Macbeth takes that to mean that no one will kill him, but what it really means is that someone who was removed from his mother's womb early will kill Macbeth.
Third Vision: The third vision tells Macbeth that he will see his end only when Birnam wood moves to Dunsinane Hill. Macbeth believes that that means that he will never fall from the throne or be killed. However, the witches have set Macbeth up to be confident in his own invincibility when really he is near his end.
Birnam Wood: Birnam Wood is a forest near Dunsinane Hill. Malcolm's men disguise themselves with tree branches so that when they approach Macbeth's castle at Dunsinane, it looks as if the forest itself is moving and their numbers are concealed.
Line of Kings: The vision of the line of kings that are Banquo's descendants shows Macbeth that it will not be his descendants who inherit the Scottish throne. But even seeing this, he does not realize that the confidence the other visions have inspired is false.