Currently, there are 2 questions using the "thin-client" tag and there is no tag description.
A thin client application is defined in Wikipedia as "simply one which relies on its server to process most or all of its business logic".
It could be argued that a Bitcoin client does the bulk of the important processing, or on the other hand that most of the processing has already been done (and stored in the blockchain).
For this reason, I personally would prefer to use the "lightweight-client" tag for those clients. However, I'll put it to a vote before I change anything.