The distinction from a restricted stock unit is the whole point, and it is not cosmetic. A restricted stock award is shares, transferred now. A restricted stock unit is a contractual promise to deliver shares later. Property can be taxed at transfer; a promise cannot, because there is nothing to be taxed on. That is why a section 83(b) election exists for one and not the other, and why the holder of a restricted stock award can be a shareholder of record with voting rights years before a unit holder receives anything.
What is taxed, and when, without an election. Section 83 counts the value of the property as compensation when it becomes substantially vested, less whatever the employee paid for it, which for an ordinary employee award is usually nothing. So each vesting tranche is measured at that tranche's own share price. A grant that quadruples in value between grant and final vest produces four separate slices of ordinary income at four escalating prices, all of it non-cash, and the employer withholds against every one of them. The employee's basis in each tranche becomes the amount included, so only movement after vesting is capital gain or loss.
Dividends are the fact most often stated backwards. Publication 525 is direct about it: "Dividends you receive on restricted stock are treated as compensation and not as dividend income", and the employer should include those payments on the Form W-2. If a Form 1099-DIV also reports them, they are listed on Schedule B with a statement that they were included as wages, and excluded from total dividends received. There is an exception that runs the other way and follows the election: dividends on restricted stock the employee chose to include in income at transfer are treated the same as any other dividends and are reported on Form 1099-DIV as usual. In other words, an 83(b) election changes the character of the dividends as well as the timing of the compensation.
A substantial risk of forfeiture is a defined thing, not a description. Treasury Regulation section 1.83-3(c)(1) makes it turn on facts and circumstances: the risk exists only where rights in the property are conditioned on the future performance of substantial services, or on a condition related to a purpose of the transfer where the possibility of forfeiture is substantial. A restriction that cannot realistically bite is not a substantial risk of forfeiture, and a grant whose only condition is a formal one may already be substantially vested at transfer.
One deferral route is closed. Section 83(i) allows certain employees of private companies to defer income on "qualified stock" for up to five years. Publication 525 states that qualified stock cannot include stock from stock-settled stock appreciation rights or restricted stock awards. So the 83(i) deferral is not a fallback for a restricted stock award holder who missed the 83(b) window.