omp parallel vs. omp parallel for
I don't think there is any difference, one is a shortcut for the other. Although your exact implementation might deal with them differently.
The combined parallel worksharing constructs are a shortcut for specifying a parallel construct containing one worksharing construct and no other statements. Permitted clauses are the union of the clauses allowed for the parallel and worksharing contructs.
Taken from http://www.openmp.org/mp-documents/OpenMP3.0-SummarySpec.pdf
The specs for OpenMP are here:
https://openmp.org/specifications/
These are equivalent.
#pragma omp parallel
spawns a group of threads, while #pragma omp for
divides loop iterations between the spawned threads. You can do both things at once with the fused #pragma omp parallel for
directive.