XY-wing
Three squares with two candidates each: a pivot "X or Y" that sees two wings, "X or Z" and "Y or Z". Whatever the pivot becomes, one of the wings becomes Z. So any square that sees both wings can forget the Z.
How to solve sudoku 5 of 6
Wings: a pivot with two wings
A wing is a little chain of three squares: a pivot that sees two wings. Whatever the pivot becomes, one of the wings gets the same digit — and so every square that sees both wings loses that digit. These are the first techniques where you no longer look within a single group.
XYZ-wing
Like the XY-wing, but the pivot holds the Z itself too ("X or Y or Z"). The Z is then surely in the pivot or in one of the wings — so only a square that sees all three loses the Z.
W-wing
Two squares far apart with the same two candidates "A or B", linked by a group where the B can only go in two places — one next to each square. So one of the two squares becomes A. Whatever they both see loses the A.