12-month rule

Accounting method

Accounting period

All-events test

Allowance method

Arm's length amount

Direct write-off method

Economic performance test

First-in, first-out (FIFO) method

Fiscal year

Flow-through entities

Impermissible accounting method

Last-in, First-out (LIFO) method

Mixed-motive expenditures

Ordinary and necessary

Payment liabilities

Permissible accounting method

Personal expenses

Reasonable in amount

Recurring item

481 adjustment

Specific identification method

Tax year

Travel expenses

Uniform cost capitalization (UNICAP) rules