Jaffa term meaning "right of leadership." If a warrior wishes to challenge a leader, his right is to call out that leader in jomo'sequ. It is intended to be a fight to the death.
In jomo'sequ the two warriors are given staff weapons (though wooden training weapons are not uncommon instead) and they fight in true Jaffa style until one emerges the victor. The practice is used among Jaffa resistance groups; it is unknown whether warriors in the service of the Goa'uld use the challenge, as the Goa'uld themselves usually appoint their First Prime and other Jaffa leaders among them.
The Warrior - Teal'c challenges Kytano to jomo'sequ after learning he has betrayed the rebel Jaffa to the Goa'uld System Lords. Teal'c wins the challenge, killing Kytano after learning he is the Goa'uld Imhotep, and becomes leader of the Jaffa resistance movement.
Birthright - Neith challenges Ishta to jomo'sequ, fearing she has lost her way in overconfidence in dealing with the Tau'ri.