The speech is generally known as "The Marshall Plan Speech," though it didn't have an official title when he delivered it. Though there were many people involved in the policy, Marshall was the Secretary of State at the time, and so he was the most visible and powerful person directly advocating this course of action. He didn't write the thing (that would be Charles Bohlen), but he gave it. It's as good a name as any.

The actual recovery plan was called the Marshall Plan, likely because the previous way to deal with Germany was the Morgenthau Plan. This kept the name theming in place, gave the credit to the guy who would take the blame if it failed, and was an easy thing to remember. The fact that both plans (all three if you throw Molotov in there) had M names is a coincidence.

The Marshall Plan is also known as the European Recovery Plan. This one is even simpler: because the goal was to help Europe recover economically from World War II.