The standard rule is a 50 percent deduction for meals that have a genuine business purpose: discussing work with a client, meeting a collaborator, or eating while traveling for business. The other half is treated as personal.
To hold up, the meal should not be lavish or extravagant, you or an employee must be present, and you should document who was there and the business reason. The IRS expects the itemized receipt, not just the card charge.
Grabbing lunch alone during a normal workday is generally personal and not deductible. Meals provided for the convenience of your business in specific situations can have different rules, but the everyday case for a freelancer is the 50 percent business-meal deduction.

