Usually found on slots games, every time a wager is placed on a progressive jackpot, a small portion of the bet is put aside into a 'pot' which grows until a specific combination of symbols triggers the prize payout.
Progressive slot machines have only been around since the technology has been available to link machines together.
Individual machines that featured a prize pot had been around for a while, but they could never accumulate enough players to really pay out significant sums, but by the mid-1980's it had become possible to connect machines from different locations.
International Gaming Technology (IGT), were the first to introduce a linked progressive jackpot in 1986, and by the time online casinos began to appear in the late 1990's, the concept was well established, and progressive titles were featured almost from the start.
With hundreds of online casinos, each with thousands of players, progressive jackpot machines have become some of the biggest attractions, and as well as slots games, you can now find progressive Poker, Blackjack, Video Poker and more, although slots remain the most widespread titles.
With a small portion of every bet, across so many casinos, the value of the prize pot can grow very quickly, with the current amount usually prominently displayed on the games' screen.
Each casino that features a game will contribute towards the jackpot, which is retained by the game developer until paid out to a winner.
The value of the prize is the same across all of those casinos, so it doesn't matter if the player is at a small site or one of the major operators, the jackpot win will be the same amount.
There are many variations on how to win progressive jackpots but with most games, special Jackpot symbols will line up across a payline, or a bonus round will be triggered during which the player must complete a certain combination to claim the win.
As soon as the jackpot is won, it is reset to a minimum level, which can still be $100,000's, and begins to grow again from there.
To qualify for the progressive jackpot, players will normally have to place a 'maximum bet' on all paylines although this also makes the jackpot amount rise even quicker.
In Blackjack, and some other progressive games, players need to make a side bet to qualify for the win, while Video Poker will typically pay out on a Royal Flush combination.