Question

What is it called when two forms of a trait are both dominant at the same time?

Answer 1

Codominance- an example is type AB blood. Both A and B proteins are present on the surface of the blood.
Incomplete dominance- an example is an offspring of a red and white flower being pink in color.

Depending on the context of your question, it's one of these 2.

Answer 2

It is call codominance