"Active Transportation" (AT) is the overall term for transportation modes that are human-powered, such as walking, biking, and riding scooters and skateboards. For the sake of distance and convenience, some professionals include transit in AT because it helps people braid together longer trips without driving their own motor vehicles: walk or bike to the bus stop; ride the bus; walk or bike to destinations; which makes bikeshare and similar systems all the more valuable. In concept, we do, too, but we offer only the most basic transit services, such as site plans for bus stops located by others.
Thus, AT includes greenways, bikeways, sidewalks, trails, and paths: any "ways" that can make it easier for people to get around their city or region under their own power, without having to drive.
AT ties very closely to recreational trails and paths, which begin to weave mountain biking, BMX biking, and horseback riding into the fabric. In some places and for some people, those modes are genuine transportation modes, and the AT network should accommodate them. Recreational trails for such modes can tie into the larger AT networks and make valuable connections.
Over the last 50-100 years, America has adopted the motor vehicle as its central transportation mode, usually to the effective exclusion of all or most other modes. Tremendous efforts, study, and expense have gone into the technology and practice of designing road networks and all of their details and impacts. Unfortunately, these efforts have swung the pendulum too far by omitting the needs of people who were not in cars or trucks. In many places, it's thoroughly impractical for most people to try to get from home to ... well, just about anywhere.
Since the 1950's and 1960's, thoughtful people have decried the imbalance in our planning and thinking, noting that cities were becoming obeisant to the needs of cars and trucks, to the exclusion of people. Now, people write about "livability" and "walkability" as keys to a city being attractive or delightful for humans, not just for cars.
In this car-centric America, we need to put in a mirroring level of effort to rebalance our transportation systems. And people want it, too. Any survey or polling on the topic will show that substantial percentages of people don't want to keep living this way: they want to be able to walk or bike to their destinations: shopping, work, church, and so on.
We need to give special attention to walking, biking, scooting, and similar transportation modes for most people to find them safe, viable, and attractive options.