Engine is a metcon class. Metabolic conditioning means training strength and cardio in the same session, working the aerobic and anaerobic systems at once: real load moving while the heart rate stays high, so you build muscle and an engine rather than picking one. A class runs in three parts, a warm-up, a short strength or skill block, then the long conditioning piece in the middle.
A good conditioning session works all three energy gears:
Immediate Powers short explosive efforts, like a heavy set or the first strides of a sprint.
Interval The middle gear, for hard efforts of one to three minutes. It is where most of a Sprint session lives.
Endurance The long gear, for steady work like the row and the run. This is Engine's home ground.
Is It the Same as CrossFit?
No. Metcon is a type of workout. CrossFit is a brand that uses it. So do HIIT and Tabata classes. Every HIIT and Tabata session is a metcon; not every metcon is HIIT. No CrossFit box required.
Engine or Sprint?
Engine is one long piece of work held at a steady effort. Sprint is short efforts repeated at an intensity you could not hold for an hour. Engine raises your ceiling and Sprint teaches you to work close to it, which is why most people here do both.
Definitions and the energy-system breakdown here line up with Healthline's guide to metcon.