In terms of finance or money.
"The company decided to cut costs financially by reducing its advertising budget."
In plain English: Financially means having enough money to pay for things and live comfortably without running out of cash.
"The company struggled financially after losing its biggest client last year."
The word financially is formed by adding the suffix -ly to the adjective financial. It entered English as a straightforward grammatical construction to describe actions done with or relating to money matters.