What is an SRS?
An SRS is basically a system for reviewing flashcards in order to optimize the learning curve. SRS stands for 'spaced repetition system' and is an increasingly common feature of learning systems and software, especially for learning languages.
Why do we need an SRS? Well, when we humans try to learn something, we tend to remember most of it (but usually not all) for a short while, then the vast majority of it just leaks away, out of our short term memory, and we retain only a tiny portion of it. This is obviously a problem if you are trying to learn something permanently, like vocabulary. The solution is to get it from our short term memory into our long term memory. That's where the SRS comes in.
How does an SRS work? Some clever people (the names Ebbinghaus and Leitner come to mind) realized that if we space out our repeated exposure to small bits of information (like on a flashcard) we can optimize the number of times we need to see it before we can recall it. Exposures come more often (an hour later, a day later), then less often (a week later, a month later) and eventually, after being exposed to something maybe as few as five or six times, it stays in our long term memory and we retain it for years. This is much more efficient than trying to bang a long list of words into your head, only to forget most of it within a few days and have to relearn them all again.
Pimsleur has made this spaced repetition a part of its language method (they call it 'graduated interval recall') and BYKI uses spaced repetitions directly as a flashcard application. The smart part about SRS in software like BYKI (as well as other SRS programs such as Anki, Supermemo and Mnemosyne) is that the repetitions are flexible according to the user. It's an optimized system for humans to learn things in general, but it can also be personally optimized to your individual learning needs.
I use both Anki and BYKI to study individual words, phrases and whole sentences, and even bits of grammar. They can even include audio and images. I have found that using an organized and systematic approach is extremely efficient. I only use an SRS about three minutes per day per language for reviewing approximately 20-40 cards, and maybe another few minutes every few days or once a week in order to input new information for review.
Using an SRS as part of your language learning regimen can be one of the most inexpensive and efficient techniques in your arsenal.