Below is a brief explanation on every type of slot machine:
3-Reel Standard Slots these are the most usual slot machines. You bet a certain amount, then spin the three reels and depending on the outcome of the spin, you either win or lose.
3-Reel Max Bet 2 Slots these machines allow you to bet the maximum of two coins, not three as in Standard Slots.
Progressive Jackpot a progressive jackpot means that a certain percentage of every bet goes into the progressive jackpot pool. You win the jackpot by obtaining a very high symbol combination, usually only when playing for maximum bet.
Bonus Game machines that have a Bonus Game require you to obtain a special symbol combination, or collect certain symbols. When you do, you will enter a bonus round, with special prizes waiting for you. Please note that in some games you have to play for maximum bet to qualify for a bonus round.
3-Line and 5-Line Slot Machines here you specify your bet per payline, and the paylines on which you bet. A payline is the line along which Your total bet is then line bet x number of lines selected. 3-Line Slot Machines have 3 lines for you to choose between, and 5-Line slots have 5.
Multiline Slot Machines same as above, only these machines have more than 5 lines, usually 8 or 9.
3-Row and 5-Row Multispin Slots this is the giant leap for slot machines. In multispin slots, after the first spin you choose which reels you want to hold, then spin the rest of the reels again. 3-row and 5-row mean you have 3 or 5 rows of reels, like in multiline video poker you have multiple hands.