Usually, brand guidelines are for everyone, while design guidelines are the subset for designers.
It varies (particularly by geography and size of organisation), but usually "brand guidelines" are the broad umbrella including:
- "Vision" or "Mission statement" etc etc
- Tone of voice and writing style guidelines
- Logo files and usage guidelines (e.g. white space, minimum size, which variants to use on what backdrops)
- Other brand assets such as letterheads, business cards and slide templates
- Colour palettes (which are used more widely than just by designers)
- Briefing documents or commissioning guidelines
Design guidelines << which are written for designers and go into detail on grids, styles, colour usage, typography, etc, and might include UI patterns, print specs, etc
- Any other specialist guidelines e.g. for video, music, product design, shop layout, customer service, responding to complaints, uniforms, company song...
Regarding the edit about UI pattern libraries - how these fit in varies as they are a comparatively new edition. They might be part of the design guidelines (e.g. this could be separated into "print" and "web"), or, they might be standalone or part of a separate document or suite on digital publishing standards aimed at not just designers and UX specialists but also content commissioners, editors, writers, IA people etc.
The latter is probably a "better" practice, as how online content is interacted with is closer to how it is planned and structured than it is to, say, print specifications; but I'm not aware of any firm standard (yet).