In common language, "flashcard" means a card with question on front side and answer on back side, used as tool for memorizing, such as foreign language vocabulary. On a computer, we can have the question be a sentence or phrase with a word missing, and the answer can be that missing word. The computer presents the missing-word question, the user types in the missing word, and the computer compares the user's answer with the correct answer, i.e. the word that was actually missing.
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But to use flashcards to effectively learn the vocabulary, you need a good system for drilling them to learn them initially then for stretching the user's memory to longer and longer timespan. My online flashcard program includes both a coach towards the correct answer (see the riddle-guessing demo for this by itself), to get the answer into the user's short-term memory, then the "all but one" (delay-doubling) algorithm for stretching that memory to medium-term (a few minutes to a couple days) and finally to long-term memory (more than a couple days).
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The online program includes separate master decks for common English words in context, English-to-Spanish translations in context, English-to-Mandarin (no context), several pre-reading exercises (single letters in context), and demonstrations of this algorithm for advertising. Before starting the drill, you need to choose one of those master decks and import some cards from that master deck into your personal deck, which will place them initially in your "input queue". After you start trying to learn a card, unless you get it right the first time, it will be in "Hurdles", or if you got it correct without help then it'll go to the "Delay queue", where it will be set aside per the delay-doubling schedule for later re-testing.
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All uses of the all-but-one online program are available via this login form. For a quick demo using a public shared account, log in as user 'guest1' with password 'free'. For serious use, ask me to set up your individual account. After you're logged in either way, select [Start 'all but one' flashcard program]. After you have some cards imported, select one of the radio buttons for finish just one card then stop, or finish entire delay-queue then stop, or delay+hurdles, or delay+hurdles+new. Then click the button to do one card and it'll proceed to successive cards if you selected anything except finish just one card. When you are about ready to quit, select the option to finish just one card, then go ahead and finish it before quitting the program.
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For people wishing to learn English (ESL or pre-school), who have already finished the pre-reading exercises, there's also a human-coach mode operated by me (or anyone else trained properly) where the coach operates the program, the program shows a word, the student reads it out loud and uses it in a sentence/phrase or tells its meaning, and the coach checks whether the student's response was correct (without needing any coaching) or not. This mode also includes pre-pre-reading, i.e. reading single letters out loud and using them as first letters of words. The whole ESL sequence is thus: pre-pre-reading letters out loud, pre-reading typing in missing letters, reading words out loud, and finally typing in missing words spelled correctly. For a demo of human-coach user-out-loud mode, you'll need to meet with me in-person.