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".
amateur: Like in sports, amateur porn features individuals who are not professional porn stars. It features ordinary individuals partaking in every day sexual acts. Girl/boy next door, wives/husbands, girlfriends/boyfriends. Sometimes real amateurs but quite often professional models just pretending.
homemade: Amateur video donne by the participat(s) with little ressources.