Your looking into it to deep. Microsoft doesn't define what a secure network is. Basically a home wireless network is one that requires a password to access the network. The level of security is a different story. Also you router is a firewall as the IP address in of PC's is behind the router which is directly on the internet.
802.11 is a set of technology standards for wireless network devices that governs the way they communicate with one another. The current home standard is 802.11 AC with 802.11N the old standard and 802.11G the standard before that.
Typically home networks have a choice of 3 protocols WEP, WPA or WPA2. Each have different levels protection quality. Meaning some are easier to hack. These protocol encrypt the wireless signal and require a password to decrypt the signal. But they are still secure because a hackers has to do something to enter get on the network. The different protocols define HOW SECURE the network is. Even the lowest level is still somewhat secure. These security terms are defined by MS they are defined by companies like Cisco, AT&T, Verizon and they send messages to Windows when there are errors.