All components that can connect into a wireless medium in a network are referred to as stations.
All stations are equipped with wireless network interface cards (WNICs).
Wireless stations fall into one of two categories: access points, and clients.
Access points (APs) are base stations for the wireless network. They transmit and receive radio frequencies for wireless enabled devices to communicate with.
Basic service set
The basic service set (BSS) is a set of all stations that can communicate with each other.
There are two types of BSS: Independent BSS ( also referred to as IBSS ), and infrastructure BSS.
Every BSS has an identification (ID) called the BSSID, which is the MAC address of the access point servicing the BSS.
An independent BSS (IBSS) is an ad-hoc network that contains no access points, which means they can not connect to any other basic service set.
An infrastructure BSS can communicate with other stations not in the same basic service set by communicating through access points.
Extended service set
An extended service set (ESS) is a set of connected BSSes. Access points in an ESS are connected by a distribution system. Each ESS has an ID called the SSID which is a 32-byte (maximum) character string. For example, "linksys" is the default SSID for Linksys routers.
A distribution system (DS) connects access points in an extended service set. The concept of a DS can be to increase network coverage through roaming between cells.
This article from : http://en.wikipedia.org/wiki/Wireless_LAN