When a UI designer designs screens, they'll also need to be aware of things like state changes or the intended outcome of clicking a button so that they can design for that.

Developers can understand technical limitations before they even start coding, which can be communicated through wireframes.

Wireframing is a quick, inexpensive way to imagine what a design will look like before any time or money is spent on development. 

All of the above.

Grids can help arrange information in a way that creates hierarchy and makes information easier to digest for the viewer.

Grids make it easier to adapt layouts for responsive web design.

Grids and gutters help make sure there is consistent padding and spacing throughout your layout.

All of the above.

Inflexible systems that dictate how to approach certain design conventions.

UI components that fit together to form units to serve a particular purpose, and can be adapted for your needs.

Standards presented by the WWW Consortium to ensure the web works the way it should.

All of the above.