I think it is a valley
In science, a three-dimensional oval is called an ovoid. Less formally, a three-dimensional oval shape is called an egg.
Deflation Hollows
There is no special name for that. You could call it "5000 square meters".
< is less than > is greater than
the name for the answer to a multiplication problem is called the product.
An odometer. Sometimes also called a pedometer.
Moving an airplane on the ground is called 'taxiing'
Sinking ground is called subsidence.
The name of the male Richardson's ground squirrel is called a flickertail. The flickertail is like a number of other ground squirrels, but they are sometimes called gophers.
West ham`s football ground is called the Boleyn Ground and its in Upton Park.
dip
A million meters COULD be called a megameter, but this name is seldom used. Instead, you would just talk about a million meters, 106 meters, or 1000 kilometers.
The ground between two hills is called a valley. A very small one can be called a gully.
Shooting or falling stars are called, "Meteors". When they hit the ground, they are called "Meteorites".
When it is above the water table, in the vadose zone, it is called perched ground water.
The cave-dwelling people in "The Lost Dark Ground" are called the Trogs.
AAMI Stadium is the name