fraternity:
(also in short: ‘frat‘; plural: ‘fraternities‘)

a fraternity of birdwatcher
an association of people having common work, interests, way of life;
a group of men belonging to a religious organisation living together under a certain set of rules; a brotherhood;
(in US & Canada; and in this context, a female fraternity is called a ‘sorority’) a society of male students, usually represented by letters of Greek alphabet,

a religious fraternity (Islam)
I am member of a fraternity of star gazers but my brother is a member of a software fraternity.
Being a member of students’ fraternity, Mike spends most of his time hanging out with the other ‘ frat brothers’ and planning some activities.
Some harmless religious fraternities are under strict scrutiny by the government because of the other more numerous banned fraternities that are involved in anti-social activities.
There are some non-religious but, more or less, sectarian or political fraternities that are looked down upon by the general public because of their selfish motives and anti-democratic activities.

a college (student) fraternity
an informative article about college fraternities, please click here,
for a news article about fraternity hazing, please click here,
for an article that discusses the several kinds of fraternities in the US, please click here
and
for a news item that shows us how we come across this word in our daily news, please click here.
