Killer Sudoku is one of the most popular Sudoku variants. The Japanese name for Killer is Samunamupure, and it is also known as Sum-Sudoku.
The puzzle has no givens, but it has the same grid format as a standard Sudoku. This grid is covered by cages, each of which enclose 2 or more cells. The cages are usually marked with dotted outlines or with separate background colors. The top-left cell is labeled with a cage sum, which is the sum of all solution digits for the cells inside the cage. Unless otherwise stated, all Killer puzzles follow the Killer Convention: all digits in a cage should be distinct. In Killer nomenclature, the boxes are often referred to as nonets.
Besides the techniques that you can use for standard Sudoku, solving a Killer requires a whole new set of solving techniques. It is often useful to know the cage combinations for particular cage sums. As an example, a cage of 2 cells with a sum of 3 has only one possible combination: 1 or 2. See this category for a list of Killer Sudoku techniques.