What is a Zone? (In the context of XenApp)

In the XenApp 5 architecture there are 6 essential components
1. Xen App Servers
2. Data collector
3. Zones
4. Data Store Database
5. License Server
6. Web Interface Server

Zones

A logical group of XenApp servers communicating with a single data collector is called a zone. Zones are typically based on subnets.

During the installation of XenApp on a server, the server must join a zone. The first XenApp server installed in a server farm defines the initial zone and becomes the data collector for the zone. The default name of the first zone is Default Zone. After the installation is complete, an administrator can create additional zones and move servers into the different zones. The first XenApp server moved into a zone becomes the data collector for that zone.

Zones can enhance the performance of a server farm by allowing related servers to be grouped, regardless of their network subnet. Zones can be used to:

Designate physical or logical groupings.
Enable zone preference and failover.

source: XenApp5 courseware

Citrix Merchandising Server, Citrix Receiver and Citrix Dazzle – Quick Overview

The short version:

Citrix Merchandising Server is a virtual appliance used to deliver and support Citrix Receiver. It is available on both XenServer and VMware platforms. It is Linux based.

Citrix Receiver – Allows users to securely access applications they need from anywhere. It installs and manages applications, securely connect users to the corporate network, and accelerates applications (video).

Citrix Dazzle – An end user interface (also, a plug-in to Citrix Receiver) that allows more flexibility for the user to select the applications they want to run on their individual devices (laptops ,desktops, Ipads and other tablets, android devices, Windows Mobile devices, etc.). It runs on top of Citrix Receiver. It works like an Enterprise App Store where the user self subscribes to whatever apps he/she needs or wants.

The long version: