Hello!

When you have three of a kind and you hold a pocket pair, it is called a set.

When you have three of a kind and there is a pair on the board (you hold the 3rd card in your hand), it's called trips.

I'm not sure if my calculations are collect, but they should be somewhat close.

P(set on flop) = 2/50 + 2/49 + 2/48 = 0,04 + 0,0408 + 0,0416 = 12,24%

Another interesting fact is: You will have a pocket pair in 0.0588 in cases. so 0,0588 * 0,1224 = 0,0072 means that if you see a flop with every pocket pair you hold, you have a probability of 0,72% to hit a set, which means that you will on average hit 7,2 sets per 1k hands, which is equivalent to 1 set every 139 hands.

Best regards,

Primzi