Best in slot

Best in slot (sometimes abbreviated as BiS or bis) is a label for any Equipment which is generally regarded as the best item that you can wear in that equipment slot for that combat style.

However, there can be several meanings of "Best in slot" as different equipment is required or strongly suggested for certain activities.

For example:

While fighting monsters with low to mid Defence, the Berserker ring(i) is the best in slot ring.

While fighting very high-level monsters with high Defence, such as the Corporeal Beast, the Treasonous ring(i) is the best in slot ring used in conjunction with the Zamorakian spear.