Final answer:
An ad-hoc WLAN is a type of wireless network where clients connect directly to each other without an Access Point. It's useful for small, direct communication tasks between devices. Other types of WLAN such as Infrastructure, Extended, and Mesh have different configurations and use cases.
Step-by-step explanation:
A WLAN formed directly between wireless clients without the use of a wireless Access Point (AP) is referred to as an ad-hoc WLAN. In this type of network, devices connect with each other directly rather than through a centralized device like an AP. This network setup is useful for small peer-to-peer activities such as file sharing or gaming. On the other hand, an Infrastructure WLAN involves devices connecting to a network through an AP, which serves as the central hub for communication. This type is commonly used in home and business networks. Extended WLAN usually involves the use of repeaters to extend the reach of an existing network, while Mesh WLAN refers to a network structure with multiple APs that interconnect to provide a large coverage area.