Can I travel to Paris for a day with a single entry visa for Schengen from Switzerland?
I am visiting a friend in Switzerland for ten days. I have already got visitor's visa for the same on my Indian passport. Particulars mentioned on my visa are: 1. 'Etats Schengen' , 2. Single entry 3. Dates of visit. & 4. Type of visa : C. I understand that having already got ‘Etats Schengen' visa, I can travel to all Schengen countries.
I am also planning to visit Paris for a day during my stay in Switzerland. However, I never mentioned this in my visa application. I am planning to take a train from Geneva to Paris and book a hotel in Paris for one night. Can I possibly plan my Paris trip this way as I have Schengen visa, or I am not allowed to travel out of Switzerland as I never mentioned this in my visa application?
Also what does Single entry on my Schengen visa means: does it mean that I can enter and leave Switzerland only once or it means that I can enter and leave the Schengen region only once.
Switzerland and France are both part of the Schengen area. Since you do not exit the Schengen area when you travel from Switzerland to France, you won't have to re-enter, thus all will be fine.
Single-entry means that you can only enter and exit the Schengen area once, in other words, every trip to the Schengen area needs its own visa.
Answering for the generic case...
There are 650 different ways to arrive/visit/depart two countries in the Schengen zone. This number doubles when single-entry and multiple-entry visas are considered.
France-Germany, Germany-France, France-Italy, Italy-Germany, France-Spain, Italy-Spain, and so on. There are too many of these to deal with on a case-by-case basis.
When three different countries are considered, the number of permutations is more than 15,000!
Regardless of which combination/permutation is selected, the same rule applies... Once you have arrived at a Schengen member and cleared immigration control, there are open borders to 25 other countries. You can visit them or catch a flight home from them.
This answer holds true for all Schengen short-stay visas except those with a specific territorial limitation specified on the face of the visa.
Single entry means you are allowed to cross an external border between a non-Schengen country and a Schengen country once (i.e. it refers to the Schengen area as a whole). You don't need a multiple-entry visa to travel through several countries within the area.
I have recently seen more frequent passport checks for trains to France starting in Geneva but the police was only looking at the ID page, not at visas.