A Chinese visa is a permit issued by Chinese visa authorities for overseas passport holders for entry into or exit and transit through the China.
In China, there are several types of visas can be issued; C, D, F, G, L, X, Z and J-1, J-2, which varied by your purpose of visit. The Chinese visa authorities issue visas according to your application, passport, identity and your purpose of entrance/visit.

C Visa
C Visa is issued to crewmembers on international aviation, navigation and land transportation missions and family members accompanying them on China-bound flight.

D Visa
D Visa is issued to applicant who is to reside permanently in China

F Visa
This is known as a business visa, F visa is issued to applicants who are invited to China for business, research, lecture, scientific-technological and culture exchanges, short-term advanced studies or intern practice for a period of no more than six months.

G Visa
This kind of issued to those who transit through China. American passport holders must obtain a transit visa to transit through all Chinese airports except the Pudong International Airport in Shanghai.

J-1 Visa
This kind of visa issued to foreign resident correspondents in China.

J-2 Visa
This kind of visa issued to foreign correspondents on temporary interview missions in China.

L Visa
The most popular type of China visa, an L visa is also known as a tourist visa. It is issued to those who visit China for tourist purposes, family visit or other personal matters.

Z Visa
It's a work visa, issued to those who are invited or hired by Chinese companies to work or teaching, and their accompanying family members.

X Visa
A student visa, issued to applicants who go to China for the purpose of study, advanced studies or intern practice for a period of more than six months.

The Validity of Chinese Visa: In general, a single entry Chinese visa is valid for 3 months from the date of issue, and a double entry visa is valid for 6 months. During the duration of owning a Chinese visa you can enter, exit or transit through China without restraint.
Duration of Stay: The duration of stay is specified on a Chinese visa. Chinese visa holders must not stay beyond the specified date without extending their visas. Otherwise, they will be subject to stiff penalties, as 500-2000 Yuan per day.
Overseas Chinese Visa Authorities: Foreign citizens can obtain a China visa from Chinese embassies, consulates, visa offices, and the consular department of the office of Chinese Foreign Ministry. For further information, please consult the nearest China visa authorities in your country.
According to the relevant international law, any sovereign state has the exclusive rights to decide whether or not to allow the foreigners to enter its territory, and accordingly to issue visa, reject visa application and cancel an issued visa according to its national law without providing the reasons.

Chinese visa application

There are different types of visas but the most common for touring China is a single entry tourist visa valid for up to 30 days from issuance that can be easily obtained through an embassy of the PRC or a CTS office.
A passport is required for visa application; the passport shall be valid for at least 6 months beyond the duration of the tour.
1. Primarily, contact Chinese embassy or consulate general in your country or region for accurate and detailed information.
2. Apply at the Embassy of the People's Republic of China in your country of residence or approach an Embassy (Consulate) of PRC in a neighboring country according to your situation.
3. Apply at an overseas CTS branch in your country of residence.
4. If you are first traveling to Hong Kong, you can entrust the visa application at a branch office of China Travel Service (Hong Kong) Limited
According to the Law of the People's Republic of China Concerning the Administration of Foreigners Entering and Leaving the Country, foreign tourists must apply for visas at China's foreign affairs offices, consulates or other organizations authorized by the Ministry For Foreign Affairs. A group of five tourists or more can apply for a group tourist visa. This is usually handled by a travel agency organizing groups. People coming to China from countries which have visa agreements with China (such as agreements which exempt tourist groups from visas) are treated in accordance with these agreements.

Visa is required for Canadians, Americans and people of most other nationalities who travel to China. You can apply it directly at the Chinese Embassies and Consulate Generals around the world:
For Canadian and US passport holders, visa is not required for Hong Kong if your stay is less than 90 days as a tourist. For the rest of other passport holders, please contact with your nearest Chinese consulate or embassy and take advices.
Besides, the Hong Kong and Macao, these two Special Administrative Region's visas have their own requirements.