Writing the source code of a program in teams of two. Also called "peer programming," each person looks at the code the other member is writing or directly after it is written. The program logic is generally flowcharted and examined by the other team member before actual coding.
The collaboration, plus the fact that each technician is validating the other, ensures that more thought goes into the writing of each routine. It also helps to make the code self documenting or, at least, better documented. See self-documenting code