What is the difference between a multi-layer and multi-tier applications?

Multi tier Architehere means Three tier or N-tier.N-Tier can have more than one tier.
Three Tier means it can have Three Tiers like
1)Presentation Layer
2)Business Logic layer.
3)Data Access layer.
1)Presentation Layer:Presentation Layer is the All User Interfaces like Asp.net pages,WPF forms,aspx pages,ascx pages
2)Business Logic layer: Business Logic layer is the what are the Functionality of the pages like Functions,events etc,All WCF is the Business logic layer.
Business Logic layer get data from the DAL.Business Logic layer it is medeater b.w PL an BLL.
3)Data Access layer:Data Access layer It can be get the data from database.

This is very common question asked by couple of companies and I noticed developers usually gets confused about the difference.

When we talk about multi-layer, we usually mean an application broken down into multiple layers such as a Database Layer, a Business Layer, and a User-interface layer. All of these layers may be seperate assemblies. For example, UI layer may have APS.NET pages, Business layer may be BL.dll and the data layer may be Db.dll. However, these all assemblies usually reside on the same machine where the application runs.

When we talk about multi-tier, these assemblies reside on seperate physical machines. In other words, there will be more than one physical machine involved in multi-tier applicaiton.