Are donations from busking (street performances) considered taxable income, or are they considered gifts?

[andrewziem]

IRS definition of gift: "Any transfer to an individual, either directly or indirectly, where full consideration (measured in money or money's worth) is not received in return."

Gifts result from "detached and disinterested generosity" and are often given out of "affection, respect, admiration, charity or like impulses" (Commissioner v. Duberstein).  Contrast payments given as an "involved and intensely interested" act.

[Carl]

Not just income, but self-employment income. The fact is, you have to  do something, usually on a recurring basis to "earn" it. People don't' just walk up to you out of the blue and say "heres a few bucks" and walk away. You provide them something in return first, in the way of entertainment as a street performer.

That would be in contract to a pan-handler to does ask for handouts for nothing in return.

[Bsch4477]

If it is a significant (I can’t put a percentage on it) source of your income you are self employed and it would be taxable as self employment income. Otherwise it is hobby income. 

[Opus 17]

Under the tax code, every dollar you receive is presumed to be taxable income unless you prove otherwise.  If audited, I think you would have a tough case here.

However, this may not be self-employment income.  If you are "engaged in an ongoing trade or business" this is self-employment income.  You must pay income tax and 15% self-employment tax on the net profit, but you can deduct legitimate and reasonable business expenses.  If this is a hobby, you don't have to pay SE tax, but you can't deduct your expenses.

More on hobby or business is here.

https://turbotax.intuit.com/tax-tips/small-business-taxes/when-the-irs-classifies-your-business-as-a...

If this is a hobby, you report it under other uncommon income, using any version of Turbotax.  If this is a business, you need a schedule C, and you have to use Deluxe or higher.  (If you are filing online and you want to deduct expenses against the income, you need the Self Employment version.)