This is the definition of usury from Noah Webster's Dictionary published in 1828-

Usury

U'SURY, noun s as z. [Latin usura, from utor, to use.]

1. Formerly, interest; or a premium paid or stipulated to be paid for the use of money.

[Usury formerly denoted any legal interest, but in this sense, the word is no longer in use.]

2. In present usage, illegal interest; a premium or compensation paid or stipulated to be paid for the use of money borrowed or retained, beyond the rate of interest established by law.

3. The practice of taking interest. obsolete

And here's the modern definition from Merriam Webster-

Definition of usury

1 : the lending of money with an interest charge for its use especially : the lending of money at exorbitant interest rates

2 : an unconscionable or exorbitant rate or amount of interest specifically : interest in excess of a legal rate charged to a borrower for the use of money

3 archaic : interest

From the KJV-

Exodus 22:25

If thou lend money to any of my people that is poor by thee, thou shalt not be to him as an usurer, neither shalt thou lay upon him usury.

Basically, you shouldn't charge interest to people who can't afford to pay it back. Payday loans are an abomination to the Lord.

Proverbs also provides this warning-

Proverbs 22:7

The rich ruleth over the poor, and the borrower is servant to the lender.