Basics

A Design Principle where transportation networks are designed to enable safe, convenient and comfortable travel and access for users of all ages and abilities regardless of their mode of transportation
Complete Streets allow for safe travel by those walking, cycling, driving automobiles, or riding public transportation
Improves Accessibility
An example would have:
Sidewalks
Bike Lanes
Standard Roads
Protected Intersections
Perhaps enhanced road managment (high occupancy lanes, bus lanes, etc)

Internal Links

The Wikipedia Page on Complete Streets
The Wikipedia Page on Walkability (Make a page on this later)
A Video on the Topic by the Youtube Channel "Road Guy Rob" (They approach it moreso from a traffic engineer's standpoint than a city planners, and thus are a bit too "large scale" perhaps? Great video either way)