TL;DR
Rent is a small SOL deposit required to keep accounts (token accounts, data accounts) stored on the Solana blockchain — it’s refundable when the account is closed.
Storing data on Solana costs SOL proportional to the account size. When you create a new token account (to hold an SPL token you’ve never held before), approximately 0.002 SOL is deposited as rent. This isn’t a fee — it’s a deposit to pay for the blockchain storage. As long as the account has enough SOL to cover two years of rent (rent-exempt threshold), the balance won’t be deducted.
If you try to send all your SOL and have token accounts, the transaction fails because you need to keep rent deposits for each account. Each SPL token you hold requires its own account with ~0.002 SOL rent. If you hold 50 different tokens, that’s ~0.1 SOL locked up in rent. This is why wallets show “usable” vs “total” SOL balance.
When you close a token account (by sending all tokens and closing the account), the rent deposit (~0.002 SOL) is returned to your wallet. Tools and wallets like Phantom allow you to close empty token accounts in bulk to reclaim rent. If you’ve traded hundreds of tokens, you might have significant SOL locked in empty token accounts. Regularly closing these reclaims rent and cleans up your wallet.