When you create a Bitcoin wallet in Electrum, you are usually given a set of words that look something like this:
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These words go by various names: seed words, seed phrase, recovery words, recovery phrase, recovery seed, mnemonic words, mnemonic phrase, backup words, backup phrase, secret words, secret phrase… In the end, they all refer to the same thing.
Typically, you will be given 12, 18 or 24 words, though this is not universal. You will be instructed to note them down, in the correct order, and store them somewhere safe where nobody but you can find them. They are of crucial importance: should you be unable to access your wallet (for instance, your hard drive fails or you lose your password), you can always recreate it with these words.
If you have lost your seed words, but you still have access to your wallet, it is possible to view them again. To do so, open your wallet in Electrum. In the menu, click on Wallet and on Seed.
You will be asked to enter your password. Afterwards, your seed words will appear:
