What is the Associated Token Account Program? Volgen
The Associated Token Account Program on Solana automatically creates a token account involving the sending or receiving of a new asset.
For example, when you send SPL-BAT to a new address, the token account program ensures that a corresponding SPL-BAT account is created for you on the receiving address. If it doesn't exist, a small amount of SOL will be spent to create and fund the new SPL-BAT token account.
You can learn more here.