repo rates determine, following, material, comment, someone

yuoska

i was working on the fixed income material last night and i was thining i can spit out some info on repos for the exam but i dont really know what they are (real life wise)

can someone give me a 2-3 line plain language expanation, or just comment of the following,

-its my understanding that, you have money lender who takes will loan you money, and then dependent on the collateral (liquid/special/how delivered...) they will determine a rate to charge you on the lent money?

-what is the collateral (securities, cash..)