yes to both.. they are hardware and most new amps have them built in with a switch that allows you to switch between low pass/mid pass/high pass.

a crossover is a frequency filter that allows a desirable frequency range to be passed to the speakers.

for instance, if you have a tweeter, you don't want low frequencies going to it because it'll buzz and sound like ass. that's where the crossover comes into play. it filters out the low frequency range and allows the high, desirable frequency range to pass to the speakers.