Think of a violin string. Bowed, it resonates with its fundamental frequency and overtones (integral multiples of that frequency). But even untouched, the string is in thermal equilibrium; by the Equipartition Theorem there's kT (it's one harmonic oscillator not Avogadro's Number of them) each in the fundamental, the 1st overtone, the 2nd, the nth, etc. Mathematically, there's no end to the number of overtones; so there are infinitely many kT additions. This means the violin string has infinite energy even before you play it?!?Fortunately not. With each higher overtone, the wavelength along the string must decrease. Eventually the wavelength approaches molecular dimensions, and since thermal energies aren't going to split up molecules or atoms, no futher shrinking of the wavelength is possible. The quantization of matter (atoms) has rendered the number of degrees of freedom of the violin string a finite (if large) number. Same for a tuba's chamber or indeed anything made of matter.
Ah, but light isn't made of matter. As of the last century, it was a continuous electromagnetic field. So it's "overtones" could, in principle, go on forever, holding infinite Equipartition thermal energy at any temperature! This was the famous UV Catastrophe wherein the equilibrium energy rose indefinitely into and beyond the ultraviolet spectrum.
Planck solved this by eliminating the continuity; he declared (correctly) that light's energy isn't continuous but rather comes in quanta proportional to its frequency. And the constant of proportionality bears his name to this day. Planck saved the Equipartition Theorem...and ushered in the Age of Quantum Mechanics.
Of course for a couple of hundred years, the world had been getting along very nicely, thank you, with good old, deterministic Classical Mechanics. And even Einstein went to his grave lamenting the loss of determinism implicit (Heisenberg's Uncertainty, remember?) in Quantum Mechanics. Einstein's telling remark about this was, "God doesn't play dice with the Universe!" But the evidence is now compelling that something does! A major theme of this course is that Statistics drives Thermo just as Thermo drives the Universe! Thus the logo.