Detonate is actually more precise, implying an explosion that accelerates at or faster than the speed of sound, often causing a visible blast wave in air that is humid and dense enough as the pressure wave compresses the air and squeezes it into visible semi cloud like formations momentarily.

RUD is a general term that can cover any number of events which cause a craft to generally lose structural integrity in a small amount of time.

For example, a craft could hit max q either at a non optimal angle, or due to structural integrity flaws, more or less violently tear itself apart.

Or, a craft could enter the atmosphere at a non optimal angle, or at too extreme a velocity, and be ripped apart, again, violently and quickly. This is generally referred to as 'Burning Up'.

Or a craft could have a parachute or landing system related problem and impact the ground at such speeds it disassembles itself. Jokingly referred to as 'lithobraking'.

Or, a craft could have an accidental triggering of some kind of abort system that results in the craft tearing itself apart.

Or, at any point while airborne, a problem with either the integrity of a fuel tank or the fuel pumps and plumbing could cause a rupture, which could then cause the craft to crumple, deform, and then rip itself apart /without/ the loose fuel igniting, or perhaps /with/ the loose fuel igniting, which may merely conflagrate or detonate depending on other factors.

While many of these more specific chains of events have more specific terms to describe them... they are /all/ Rapid Unplanned Disassemblies.

All that that term means is for some reason your craft went from being more or less one piece to more or less a large number of pieces very quickly.

For example the Challenger disaster was a RUD. But not a detonation. Detonation is more specific and I used the term for a reason.