There is no such thing as a true random generator when we are talking about software - hence the P in PRNG. The seed value to any of these algorithms is meant t

There is no such thing as a true random generator when we are talking about software - hence the P in PRNG. The seed value to any of these algorithms is meant to be the "true" random part - or as close to that as it can be. The idea here is that given a truely random seed, the algorithm should subsequently generate random bits that aren't predicable from its last output. So given the first 128 bits of output you shouldn't be able to predict the next bit for example. Given the same seed a PRNG, and a CSPRNG will always output the same bits. Hopefully that explains it?