A flash card can be used to collect and store a small amount of information, to help memorising bits of information. It usually contains a question related to a fact on one side and a response in form of a brief fact on a specific subject on the other side. Flash cards can be both physical and virtual.
Teachers or students can get complete set of flash cards on existing topics (for example the Quizlet's library here) or make their own flash cards with a bit of paper or cardboard. There are also many free online flash card creation sites available. The process of creating flash cards yourself (as opposed to getting ready-made ones) has the added advantage of already revising the learning materials and thus retaining the knowledge even better.