If you have a cryptocurrency wallet, you were most likely instructed to keep a phrase of 12 or 24 randomly-chosen words in a safe place. This very combination of words is a seed phrase.
This phrase, as well as your private key, allows you full access to your wallet (although the seed phrase is not the same as the private key). You need the private key to confirm (or, so to say, ‘sign’) your transactions, but often you don’t even know what it is – the crypto wallet signs your transactions for you with your private key. As for the seed phrase, you can see it when you generate your wallet, and this is when you are supposed to note it and keep it in safe place. You can also use it when you need to restore your wallet, for example, on a different device.
Actually, you don’t need to know all this to use cryptocurrencies. You need to remember one thing – never and under no circumstances can your seed phrase (as well as the private key) be disclosed to anyone. There can be only one exception: when you want to give another person access to your wallet. Anyone who knows your seed phrase or your private key has your wallet in their full possession and can control all the cryptoassets in it.
Here’s a question: why not to use a long, complicated password of randomly-chosen symbols instead of the seed phrase? The answer is quite simple. With a complicated password, there are more opportunities to make a mistake, such as mixing up symbols. The price for a mistake in the crypto world is high. It is much easier to use regular words in a certain order and allow your wallet source code to generate the keys.