Bhiksu == 比丘
A monk, who has left home, been fully ordained, and depends on alms for a living.
Bhiksuni == 比丘尼
A nun, see also Bhiksu.
Five Bhikshus == 五比丘
The first five of Buddha”s converts: Ajnata-Kaundinya, Asvajit, Bhadrika, Dasabala-Kasyapa, and Mahanama-Kulika. They were the first five disciples that Shakyamuni preached when he became Buddha.