The term imayo denotes a wide rubric of popular song, which could even include regular waka, and a specific type of song, only ten of which are extant in Ryojin hisho. In the narrow sense, imayo proper knows a limited set of prosodic possibilities, often in the form of a quatrain, that follow an alternation of eight and four syllables. The three main genres that survive in Ryojin hisho are Buddhist song, deity song quatrains, and deity song couplets. In fact, within the two extant categories of "deity songs", many lyrics deal with the topic of love and yearning. Whatever the theme of an imayo, the majority of songs take their cues from the lives of the Heian lower classes. The second half of the twelfth century saw the rise of a new type of female performer, the shirabyoshi. The term at first denoted only a type of song; later it came to refer also to its singers.