Form 510 is Maryland's Pass-Through Entity Income Tax Return. This is the form used by partnerships, LLC, and S corporations to report income and expenses that ultimately passes to its owners. Use this form for standard pass-through reporting.
Form 511 is Maryland's Pass-Through Entity Election Income Tax Return. This form is used when a pass-through entity elects to pay tax on behalf of its nonresident members. Use this form if you're electing to pay tax at the entity level on behalf of nonresident owners.