On a boat or a ship, the engine room is the place where the engines are.
2. countable noun
If you refer to something as theengine roomof an organization or institution, you mean it is the most important or influential part of that organization or institution.
These firms are regarded as the engine room of the British economy. [+ of]
engine room in British English
noun
a place where engines are housed, esp on a ship
Examples of 'engine room' in a sentence
engine room
What we are trying to look at here is the engine room of the economy.
Times, Sunday Times (2014)
Governments equally want schools and universities to act as the engine room of the economy, turning out citizens with useful skills and qualifications.
Paul Martin MAKING HAPPY PEOPLE (2005)
OUR small and medium-sized firms are the engine room of our economy.