What does mean when scientists say the earth wobbles?
It wobbles like a child's top does but on a longer time scale.
Every 27,000 years the Earth does a kind of wobble, called precession, much like a child's top or a gyroscope. This means that the amount of solar radiation that reaches the northern hemisphere in particular, varies. This wobble is one of three factors related to glacial/interglacial cycles on Earth.