What is seed?

Computers aren't able to produce random numbers, instead they produce a sequence of numbers which repeat very infrequently - this number is usually very large with any good random generator, e.g. after digits. In addition is you look at any smaller sequence then it'll look entirely random.

Where you are in this sequence is the seed. Therefore if you reset the seed to the same value each time before generating random numbers, then you'll recreate the same sequence each and every time.

Because you often don't want this, a lot of people use the system clock to set the seed. This approach is nearly perfectly random in its initialization, because when a program starts is usually determined by some user action - and humans are very random!. In the example at the top of this page, they used.

Stats::Dists::Discrete::Poisson::RandomSample B(61.47, time(0) / MERSENNEDIV);

where time(0) is the system time and MERSENNEDIV is just a constant that reduced the return from time() to something between 0 and 1.