The one of the two
strands of
DNA that is read by
RNA. The
double helix is locally unwound, and the growing chain of
mRNA takes the place of the unwound strand. It uses
RNA polymerase to add to itself at its
3' end as it goes along the
gene. It begins doing this at the
promoter site and stops at the
terminator site.
The template strand is considered to be antisense, because the mRNA it makes is complementary to it but identical in sense to the other DNA strand.
Which strand of the DNA is taken as the template depends on which direction the promoter site points. It differs from gene to gene. There are even cases of genes encoded on opposite strands at the same point.