Single-entry visa allows only one entry to the country. Once you leave its territory, you have to apply for new visa to be able to return. For most of the trips and holidays, this is enough and if one country offers multiple versions of the visa, the single-entry visa is usually cheaper and faster to obtain.
Multi-entry visa allows you to enter and leave your destination multiple times during its validity without applying for a visa or travel registration. Be aware that usually each visit is limited by certain amount of days which you cannot exceed. Also, some countries might still limit the number of entries. Always check the details before applying.
Single entry visa allows you to enter the country just once during its validity and if you want to come back, you need to apply for the visa again. While multiple entry visas allow you to come back multiple times. But be aware, there are also some visas allowing only 2 or 3 entries.
The multiple entry visas cost more usually, but both price and visa types differ country by country. Choose the country you plan to visit and see the pricing details for each visa in the upper table.
The multiple entry Schengen visa covers all members of Schengen area and is valid for 1, 3, or 5 years. Countries included are Austria, Belgium, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, and Switzerland.