What does MECO mean?

It is the end of the first stage’s job. Everything goes suddenly quiet, and for a few seconds the whole stack is coasting at about 8,300 km/h.

Separation follows four seconds later, at T+2:30, which is deliberate: the gap lets the engines finish shutting down before the two halves are pushed apart, so the upper stage lights in clean air rather than into an exhaust plume. The second stage ignites seven seconds after that, at T+2:37.

The obvious question is why the engines stop while there is still fuel in the tank. Two reasons. A returning booster has to keep enough propellant for the entry burn and the landing burn — a landing is not free, and it is paid for out of the same tank. And the rocket is getting lighter every second, so the same thrust produces more and more acceleration; cutting off caps the g-load on the structure and, on crewed flights, on the people.

This is also why the same rocket can lift more when it is thrown away. A Falcon 9 carries 22,800 kg to low orbit if the booster is expended, but 18,500 kg if it flies home — the difference is landing fuel.

You will also hear SECO — Second Engine Cutoff — when the upper stage shuts down having reached orbital speed. On this flight that is at T+8:39, about 210 km up and travelling at roughly 27,000 km/h. MECO ends the loud part; SECO ends the climb.