What's the difference between a religion and a cult?

The amount of people that believe in it. 

"Religion" means "a religious organization I understand and respect". "Cult" means "a religious organization I am largely ignorant of".

Since you appear to mean a toxic cult, the difference is that toxic cults use brainwashing techniques, try to get all your money and possessions, and build up a cult of personality around the leader.  They usually involve sexual sin, too.

ONE is of the truth and rightness and the other is of lies and deceit. 

The definition of "cult" is somewhat ambiguous, so I have my own personal definition.

A cult coerces and pressures people who wish to leave the cult, usually through some sort of ostracism.

In true Christianity, if a Christian wants to leave the faith, then they are considered an "outsider" and thus can be fellowshipped with (1Cor 5).

A religion usually involves a deity of some kind but a cult has a human leader who has declared himself as being something that he isn't.  Cults are very difficult to escape from.  God's don't try to stop you from leaving a church.

Actually, they mean the exact same thing, but "cult" nowadays usually refers to negative groups that often kill themselves or people who give away ALL their money to the group. "Scheme" and "plan" mean the same thing, but "scheme" has a negative connotation in North America.  One never sees terms like "housing scheme" in NA, just "housing plan".

Religions are just cults that are more accepted by society. 

Usually just longevity...

Religion is socially acceptable. Every religion started as a cult.