What is network and system hardening?

What is network and system hardening?
What is a firewall?
Are there different kinds of firewalls (not manufacturers of firewalls, different types of firewalls)?
How do firewalls work?  Should you drop or deny requests when configuring a firewall?
What is a blocklist (previously referred to as blacklisting)?  Allow-list (previously referred to as Whitelisting)?
What is a proxy?
What is an IDS?  An IPS?
What is the difference between passive and active scanning on a network?
What is spoofing?
What is war driving?
How do you close ports?
What is hacking?  What is a white hat (ethical) hacker?  A black hat (un-ethical) hacker?  Gray hat?What is social engineering?
What is virtualization?  What is a guest OS?  A host OS?
What is a hypervisor?  What is the difference between Type 1 and Type 2 hypervisors?
What is a VPS?  A VPN?  A VLAN?  SDNs?
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