For tax purposes, travel expenses are the ordinary and necessary expenses of traveling away from home for your business, profession, or job.

Per IRS Publication 463 Travel, Entertainment, Gift and Car Expenses, page 2:

You may be able to deduct the ordinary and necessary business-related expenses you have for:

• Travel,
• Non-entertainment-related meals,
• Gifts, or
• Transportation.

An ordinary expense is one that is common and accepted in your trade or business. A necessary expense is one that is helpful and appropriate for your business. An expense doesn’t have to be required to be considered necessary.