( https://debianforum.de/forum/viewtopic.php?f=30&t=56194 )
The mode can be:
Ad-Hoc (network composed of  only  one  cell and  without  Access  Point),  
Managed (node connects to a network composed of many Access Points, with roaming), 
Master (the node is the synchronisation master or acts as an Access Point), 
Repeater (the node forwards packets between other  wireless  nodes),  
Secondary  (the node  acts  as a backup master/repeater), 
Monitor (the node is not associated with any cell and passively monitor all packets on the frequency) or Auto.

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introduction_to_wifi_0
======================

see: https://tavaana.org/sites/default/files/introduction_to_wifi_0.pdf ( mit Struktogramm ! )

*** Master Mode
Master mode (also called AP or infrastructure mode) is used to create a service that looks like a traditional access point. The wireless card creates a network with a specified name (called the SSID) and channel, and offers network services on it.Wireless cards in master mode can only communicate with cards that are associated with it in managedmode. 

*** Managed Mode
Managed mode is sometimes also referred to as client mode. Wireless cards in managed mode will join a network created by a master, and will automatically change their channel to match it.Clients using a given access point are said to be associated with it. Managed mode cards do not communicate with each other directly, and will only communicate with an associated master.

*** Ad-hoc Mode
Ad-hoc mode creates a multipoint-to-multipoint network when there is no master or AP available.In ad-hoc mode, each wireless card communicates directly with its neighbors. Nodes must be in range of each other to communicate, and must agree on a network name and channel.

*** Monitor Mode
Monitor mode is used by some tools (such as Kismet) to passively listen to all radio traffic on a given channel. This is useful for analyzing problems on a wireless link or observing spectrum usage in the local area.Monitor mode is not used for normal communications.