DNA polymerase

Extension rate

 * How rapidly a particular DNA polymerase enzyme synthesizes a complementary strand.

Processivity

 * A measure of how strongly the polymerase binds to template DNA. Processivity doesn't affect extension rate.  However, it has a strong influence on the absolute length of complementary DNA strand that can be made.

Proofreading

 * Proofreading is when the multi-functional enzyme adds a deoxynucleotide and then goes back and rechecks the template to complement interaction to make sure the correct nucleotide was added.
 * Proofreading polymerases are usually multimeric and thus more expense to make.
 * Like all DNA polymerases, proofreading polymerases add an adenine deoxynucleotide to the 3' end of the complementary strand. Proofreading ensures that this nucleotide is removed again leaving blunt-ended DNA.