Also known as a mark or an icon, your logo is the visual identifier for the company or product in its simplest form.
Here's an analogy.
If a person is a brand, their logo is their face. The face is usually the most distinctive visual characteristic that comes to mind when you think about them.
Why does it matter?
Your logo is the defining image that comes to mind when people think of your company and your digital product. It helps your business quickly differentiate itself in market and sets a tone for the type of visual presence you want to convey.
How does it apply?
Depending on the type of digital product and industry, logos play varying roles. For consumer products, the logo must display well in an app icon and browser favicon as well as the product site. It may also inform UX patterns. In B2B businesses the logo plays a smaller role in the product, but is important for product marketing efforts to create familiarity and differentiation.