Unlike other blockchains, Solana requires you to create a new address for each token you own. This creates two problems for users:
Users can have multiple accounts containing tokens, fragmenting user balances.
Users cannot receive tokens unless they have a token account.
Solana's solution to this is associated token accounts: accounts that are associated with a user's main wallet address. However, some dApps such as Raydium, were created before this solution existed and some token accounts must now be migrated.
If you have token accounts in your wallet that need to migrated to associated token accounts, you can use the migration tool on this page to simplify the process of moving your balances over.