What is the correct term for changes in the elliptical shape of Earth's orbit every 100,000 years?

The correct term for changes in the elliptical shape of Earth's orbit every 100,000 years is

Milankovitch cycle

Explanation:

Milankovitch cycle was discovered by Mr. Milutin Milankovitch, who described that there occur changes in the earth's orbit in 3 cycles which are distinctly of different lengths.

There occurs changes in the shape of the earth's elliptical orbit from minimum to maximum and comes back to the minimum, which takes near about 100,000 years.

The tilt of the earth is about 23.5°, which changes from about 21.5° to 24.5° and gain goes back about 41,000 years approximately.

The imaginary internal axis of the earth rotates unsteadily with a period of nearly 23,000 years.

Thus, these changes occurring in the earth's elliptical shaped orbit takes place every 100,000 years and is a cycle of the Milankovitch cycle.