A walk-in closet is large enough to allow one or more people to open the door and walk into the space to access clothing. A reach-in closet only lets you open the door to reach in to access clothing.
Oftentimes both sides of the closet and the far end are filled with rods and storage for clothing and there’s a small “walkway” measuring at least a few feet wide that lets you walk into the space.
Having a small walk-in closet in your bedroom makes it necessary to streamline your belongings and optimize functionality so that you can keep your wardrobe organized and accessible.