By many accounts, the origins of sweepstakes are actually deeply tied up with the world of gambling, starting in areas where casinos and the like were simply not possible. The two concepts share a lot of common features, particularly around the idea of chance, but what are the key ways in which they differ?
Casino Prizes
Having things like events, contests, and competitions in online casinos is one of the core features of the whole industry. Whether they are tying them into slot games, table games, live casino games or even sportsbook betting in some cases, there are always events going on. All the prizes crucially have some kind of cash money value, even with things like free spins.

Big events with big cash prizes are the flagship, however. Whether those are being paid through PayPal in casinos in the UK and around the world, or directly by bank transfers in the US, these prizes often go into the thousands or tens of thousands at the top level. The core difference here is that these prizes require some form of ‘entry fee' to go for, usually meaning real money wagers being placed.
Sweepstake Prizes
By comparisons, sweepstakes have to be, by definition and usually by law, without a cost to enter. Sweepstakes have to be either completely free to enter by just providing contact information or have an entry requirement that is some kind of task or challenge. Challenges could be something like a free mini-contest, a quiz, or some other task, but those must be open to everyone.

Thanks to this requirement, it's more common for prizes to be products or experiences rather than direct cash prizes. That's not to say that cash prizes are especially rare. In general, though, you'll see car manufacturers offering cars, food producers providing food, and entertainment venues offering holidays.
The Middle Ground
There is a concept known as a sweepstakes casino which can make the whole thing a bit more confusing. A sweepstakes casino takes concepts from both camps, using games like slots and poker but having the requirement of free entry. This is achieved by using virtual currency in place of real money for the casino games which then pay out in the same currency. This is much in the same way that video games like FIFA titles and others use in-game currencies for purely in-game rewards.
The sweepstakes then come into play with a kind of ‘premium' currency, earned in much the same way as other contests are entered. Popular choices involve participants following social media pages, making social posts of their own, or any number of small tasks like that to earn tokens which allow them to then enter sweepstakes. It's a combination concept that still sticks to the sweepstakes rules.
Overall, the contests above all come down to one core factor: luck. By design, the results must come down to pure chance, and that's usually one of the biggest parts of the appeal!