Short-term memory is like a receptionist for the brain. It's responsible for registering information temporarily and determining whether it will be dismissed or transferred on to long-term memory. Although it can sound complicated, this sorting function takes less than a minute to complete. For example, it is helping you right now make sense of this sentence by storing information from the start of it until you've finished reading the end.
More recently, scientists have begun to dive a little deeper into "short-term" brain functions and have added a separate (but similar) type of memory, known as "working" memory. Although the two are often used interchangeably, they are different. Working memory emphasizes the brain's manipulation of information it receives (using it, storing it and so on), while short-term memory is a more passive concept. Working memory is often thought of as the brain's "scratch pad," which keeps information — such as a number or name — on hand just long enough to use it.
As we grow older, the length of time our short-term memory can store information becomes shorter. This makes us more likely to have trouble keeping up with certain tasks, like remembering which button to push in a bank's phone menu. It also gives our brains less time to successfully move new information to long-term memory, making us more likely to forget details of recent events. Memory lapses and cognitive decline are a normal part of aging, but not an inevitable one, you can work to slow down the process by maintaining a brain-healthy lifestyle and keeping your memory active.