This question has not yet appeared in my inbox, although since I have already written an explanation on the meaning of the term “Sniffer” it makes sense to write one about a tool commonly used in conjunction with a “Sniffer”. So here is an explanation on what a “Scanner” is and what it may be used for. Note I am referring to a “Network Scanner” not an optical scanner.
A “Scanner” is a shortened term for “Network Scanner”. The “Network Scanner” is a software program that can be used to passively scan for network broadcasting devices, such as a wireless access point (AP) that could potentially be exploited in order to gain unauthorized access into a system belonging to the network connected to this wireless access point, or perhaps authorized access assuming you have permission from the owner of the network or computer to perform a security audit.
By using the term “Passive Scan” I am referring to a scan in what is commonly known to security enthusiasts as a scan in “Monitor Mode”. This means that the wireless device will only capture data packets and broadcast beacons without sending and data packets. Thus making you much less likely to be discovered by the owner of the device or devices that you are collecting data packets from. I would also like to note that in most circumstances collecting wireless packets should be no more illegal than say peering into your neighbour’s lounge room through the front door that he left open. It is in principle no different. Just be sure that if you do choose to pursue the data packets of your surrounding access points that the owner of them is not a security freak or a person with a great lawyer, as this could result in them turning the tables on you and getting you in trouble.
Due to the haze between the terms “Sniffer” and “Scanner” personal opinions on each may vary. My preference in network sniffers would be Wireshark and my preference in “Scanner” would be Airodump-ng.
I hope that this has helped you understand the meaning of the term “Scanner” when referring to network security. Have fun testing your network from the outside, perhaps it is not as secure as you may have once thought.