(verb)
to take money from an institution such as a bank or a person, with the intention (and often a formal agreement) of paying it back, sometimes with interest;
e.g. She plans to borrow money from a bank to help her pay for a new car.
(verb)
broadly, to take something from a particular source and use it for one's own purposes, for example to use a method or idea in one's own work or to adopt a word from one language to be used in another;
e.g. I decided to borrow their technique because it seemed to be more effective than mine.