What is Max Q?

A rocket leaving the ground faces two things that pull in opposite directions: it is speeding up, which increases the force of the air on it, and it is climbing into thinner air, which decreases it. Early on, speed wins. Later, thinning air wins.

Max Q is the crossover — the peak of that curve, and the point of greatest mechanical stress on the airframe. Rockets are built to survive it and no more, because building for a load that never happens is wasted weight.

It is why you often hear the engines throttle down shortly after launch and then throttle back up. Easing off through the roughest part of the ride is cheaper than making the structure stronger.