If written with capital letter (Central Europe), it means a cultural region, traditionally including countries between France and Russia. It can be understood as fluid, but generally makes sense on many levels and includes:
Germany, Poland, the Czech Republic, Switzerland, Austria, Ukraine, Hungary, Belarus, Slovakia, Liechtenstein, Luxembourg...
In geographical meaning (central Europe), most Central European countries (like Switzerland, Poland or Germany) are entirely and quite deep in western Europe (geographically). The meaning of the word "central Europe" becomes a bit more fluid (depending on a definition of a centre), but usually includes: Lithuania (centre of gravity), Hungary (geometric midpoint), Estonia (if all the islands of Europe – from the Azores to Franz Joseph Land and from Crete to Iceland – are taken into consideration). You can call all countries around it (to a certain radious) central European.
A common mistake is to relegate c/Central European countries into "E/eastern Europe". That is offensive and ignorant not only for people in or from the countries but also well-educated people elsewhere.
Central Europe is the first place in the world where the first wholly web-based bank succeeded.