A monde is a ball-like object located near the top of a crown. It is the point at which a crown's half arches

Half-arch (crown)

A half-arch is the piece of gold, silver or platinum, usually decorated with jewels, that links the circlet of a hoop crown to the globe at the top of the crown.-British tradition of 4 half-arches:...

 meet. It is usually topped off either with a national or religious symbol, for example a cross

Cross (crown)

A cross is the decoration located at the highest level of a crown on top of the monde. Its usage traditionally symbolised the Christian nature of the monarchy of that country, though not all crowns even in monarchies associated with Christianity used a cross as its top decoration, with some French...

 in Christian

Christian

A Christian is a person who adheres to Christianity, an Abrahamic, monotheistic religion based on the life and teachings of Jesus of Nazareth as recorded in the Canonical gospels and the letters of the New Testament...

 countries.

When the crown is worn as a circlet

Circlet

A circlet is a crown with neither arches nor a cap ....

, the half-arches, monde and cross detach as a unit.

The monde can clearly be seen as the jeweled ball, just below the cross, in the image of St Edward's Crown opposite.