A chart of accounts is the master list of categories your bookkeeping uses — every account into which income, expenses, assets, and liabilities are sorted. For a rental it typically includes accounts like rent income, repairs, management fees, insurance, mortgage interest, and security deposits held (a liability, not income).
A well-built chart of accounts is what makes reports and taxes fall out of the books cleanly: when each transaction lands in the right account, your owner statements, Schedule E categories, and profit-and-loss come together without reclassifying entries by hand. Mapping your accounts to the tax lines you’ll ultimately file against saves the most work at year end.