Everything on Solana Is an Account (The Account Model)

// Every account on Solana has this shape:
pub struct Account {
    pub lamports: u64,            // SOL balance (1 SOL = 1e9 lamports)
    pub data: Vec<u8>,            // arbitrary binary data
    pub owner: Pubkey,            // the program that may modify this account
    pub executable: bool,         // true for programs, false for data
    pub rent_epoch: Epoch,        // legacy; mostly unused post-rent-exemption
}

// Example: a USDC SPL Token mint account
//   lamports:   ~1.46e6 (rent-exempt minimum for size=82 bytes)
//   data:       82 bytes = [supply: u64, mint_authority, decimals, ...]
//   owner:      TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA (SPL Token program)
//   executable: false

// Example: a user's USDC token account
//   lamports:   ~2.04e6 (rent-exempt for size=165 bytes)
//   data:       165 bytes = [mint, owner, amount, delegate, state, ...]
//   owner:      TokenkegQ... (the program "owns" the data layout)
//   executable: false

// Note: every account's data is interpreted by its owner program. A user
// can't write to an account they don't own unless the owner allows it via
// CPI (Cross-Program Invocation).