They're called "rings". They don't have a specific name - they are part of the habit and signify those women who have taken their perpetual vows.
Some orders of nuns wear a wedding ring as a symbolic "marriage" to Jesus and their faith. Nuns are not God's wives.
the fear of nuns is called "monachousaphobia"
A gathering of nuns is called a nunnery. Or a convent.
Nuns
Those who helped slaves escape to freedom were called abolitionists or conductors on the Underground Railroad. They provided shelter, food, and safe passage to those seeking to escape slavery in the United States.
In some traditions, novice nuns may wear a plain ring as a symbol of their commitment to their spiritual path, similar to a wedding band. However, this practice varies between different Buddhist sects and is not universal.
Girls who were training to be nuns would be postulants when they start, and then novices. The Catholic Orders do not allow boys to be nuns or sisters.
Nurses are NOT typically called "sister or sisters", and would likely be seen as a put down in the US. However, many Nuns train to be nurses. Because they are Nuns, they are called Sisters.
Mary founded an order of nuns called the Sisters of St Joseph of the Sacred Heart.
Sisters of Charity
prior
Yes; they are called "Brides of Christ".