Equity method
The accounting used when a company owns a large minority stake, usually 20% to 50%, and has real influence but not control. It books its share of the other company's profit or loss as one line in its own results, and the value of the stake moves up or down with it.
Simple example
A company owns 25% of a partner. The partner earns $40, so the company adds $10 to its own profit and raises the stake's value on its balance sheet by $10. If the partner loses $40, the company records a $10 loss.