Umm.. his question was simply "What is a synthesized receiver". Nothing said about a beginners radio in the OP.

We try to enforce frequency control, but often times, people show up alone, then just fly. Later on, someone will show up and fly and one has a frequency pin, one does not. If they both opted not to take the pin, and they were both on the same frequency... well, you said it, didn't you... poor practices. It can be very hard to enforce so it has to become a habit.