classical physics
Classical physics is the grand body of theory built up before about 1900, resting on two towering achievements: Newton's mechanics, which describes how forces move matter, and Maxwell's electromagnetism, which unites electricity, magnetism, and light into travelling waves. Together with thermodynamics they explained an enormous range of the everyday world — falling apples, orbiting planets, electric currents, and the colour of a rainbow.
Its picture of nature is reassuringly definite. Particles have a precise position and velocity at every instant; if you knew them all exactly, you could in principle predict the future without limit. Light is a continuous wave that can carry any amount of energy you like, and quantities such as energy can take any value along a smooth, unbroken range. Nothing in this world comes in indivisible lumps.
This framework is magnificent and still governs bridges, satellites, and circuits today. But aimed at the very small — atoms, electrons, and individual rays of light — it began to give answers that were not just imprecise but plainly absurd. The failures gathered around heat radiation, the stability of atoms, and the behaviour of light, and out of that crisis quantum mechanics was born. Classical physics is best seen not as wrong but as the large-scale limit of a deeper theory.
The pre-quantum toolkit: superb for the everyday world, but it breaks down at atomic scales.
Calling classical physics 'wrong' is too harsh. It remains exact in the limit of large objects and slow speeds; quantum mechanics must reproduce it there, which is the content of the correspondence principle.