Engr_mech, You wrote:
"What is meant by "standard pipe".........?"

It depends on the context and basis behind the question.

What might be the standard pipe used in one type of plant may not be the standard that is used in another type of plant.

Some processes require Glass Lined Pipe, that is the "Standard" for that plant. Another process may use all Aluminum Pipe so that is the "Standard" for that plant.

What type of plant and process are you involved in that causes you to ask this question?