A template strand is the term that refers to the strand used by DNA polymerase or RNA polymerase to attach complementary bases during DNA replication or RNA transcription, respectively; either molecule moves down the strand in the 3' to 5' direction, and at each subsequent base, it adds the complement of the current DNA base to the growing nucleic acid strand (which is thus created in the 5' to 3' direction).
Because this new strand is created by complementarity, it matches the opposing strand of DNA, which is called the coding strand. The simple figure below illustrates the process of RNA transcription, in which thymine in the coding strand is replaced by uracil in the growing RNA strand, but all other bases are identical.
