webcam: Type of videos captures via webcams, often on sex video-chat sites or sex cam streaming sites. Those almost allways implies an "amateur" dimention.
cam: Videos captured by a non-professional camera. This can be a surveillance cam, a webcam, a nanny cam...
solo: Can be a video with just one performer, often masturbating or flashing. Solo can also be associated with another term, like "solo female" - a girls only scene, or "solo male".