Many times we use Layer and tier simulatneously while explainging any architectural things in problem domain.
Somewhere on the web I got a very nice differentiation which seems to get the meaning behind these words.I thought its good to share this with you here..
difference between a “layer” and a “tier” A “layer” is a logical representation, whereas a “tier” is a physical representation. This means that a layered framework can reside on one sole machine — i.e. the DataAccess, Business and Presentation code reside on the same machine — or we can spread each layer to another machine so that you get multiple physical “tiers.”