The seed phrase is a set of words that allows you get access to funds of your Waves account. During account registration, you will be always asked to save your secret phrase (Seed) which contains 15 English words with spaces between each word.
Open online or desktop Waves app and click on the Account avatar at the top righ corner. Then click on the Settings. Account seed phrase can be found under Settings > Security > Backup phrase.
For example, a standard seed phrase looks like this:
uncle push human bus echo drastic garden joke sand warfare sentence fossil title color combine
And it will always generate the same Waves address: 3P9KR33QyXwfTXv8kKtNGZYtgKk3RXSUk36
How it looks like in the Waves app:
If you are importing the seed passphrase and you are getting a completely different Waves address. In this case, there are some changes in the imported phrase. In other words, one seed phrase will always generate only one Waves address. If the address is different, it means that the phrase has differences in at least one character. For more information, please check the folowing article