In the English language, the word "occupation" has several different meanings. 

In regard to the content of the webpages on our http://twdefense.info/trust3/ website, and the territorial issues discussed therein, we primarily need to distinguish two different meanings of the word "occupation."

Occupation of Unpopulated Territory

(I)

[CLASS A] Occupation may be spoken of in relation to islands or other territory with no population. Islands or territory of this type are often referred to as "terra nullius."

terra nullius -- [spoken of unpopulated territory] uninhabited islands or lands.

Generally speaking, people from other areas who move into such islands or territory may be said to occupy it. In other words, they have become residents; they are dwelling in, staying on, and inhabiting such lands or territory. They may hope to establish a permanent presence there in the expectation that some day in the future they may claim sovereignty in the name of their own country.

It must be noted however that under international law, the process of acquiring internationally recognized sovereignty over such areas is not entirely clear.

[CLASS B] A similar situation may occur in regard to areas which appear to have no population, but where wandering tribes, itinerant nomads, aboriginal groups, indigenous people, etc. (hereafter "itinerant natives") make regular visits, even to the extent of establishing temporary settlements therein. 

Often seen is that areas of this type have the characteristic of lacking a central government.

Such lands or territories can be referred to as "terra sine domino."

terra sine domino -- [spoken of populated territory with a very low population density or lacking long-term established settlements] "land without master," land with no central government or no established governing authority, abandoned territory, land where the "owner" is unknown. 

Generally speaking, people from other areas who move into such lands or territory may be said to occupy it. To put this another way, they have become residents; they are dwelling in, staying on, and inhabiting such lands or territory. They may hope to establish a permanent presence there in the expectation that some day in the future they may claim sovereignty in the name of their own country. However, this will certainly bring them into conflict with the itinerant natives.

It must be noted however that under international law, the process of acquiring internationally recognized sovereignty over such areas is not entirely clear.

Military Occupation

(II)

The second type of occupation is spoken of in relation to foreign military control of territory. It is termed "military occupation."

Generally speaking, soldiers and other military personnel who travel from their own country and enter into other lands or territory may be said to occupy it.

Military Occupation -- (1) invasion, conquest, and/or control of a nation or territory by foreign armed forces, (2) a condition in which territory is under the effective control of foreign armed forces, (3) the military government exercising control over an occupied nation or territory. 

Importantly, 

• International laws states that military occupation does not transfer sovereignty. 
• There is no recognition of any transfer of sovereignty at surrender ceremonies, or as the result of surrender ceremonies.
• Military occupation is not annexation.
• For territory under military occupation, the doctrine of "prescription" cannot be applied in order to justify a claim of ownership.
• The internationally recognized laws of war specify many types of activities which are prohibited in occupied territory.  Important references in this regard include the 1907 Hague Regulations and the 1949 Geneva Convention (IV). There is also a substantial body of customary law that is binding on all states and parties to a conflict.
• Legal relationships in occupied territory are based on a consideration of "Who is the occupying power?", which may also be phrased as "Who is the legal occupier?"  
• The determination of the legal occupier typically comes down to verifying which country’s military troops liberated the territory, or which country’s military troops played the major role in such liberation, or which country was considered the principal victor. 
• Military occupation is conducted under military government. In other words, military government is the form of administration by which an occupying power exercises government authority over occupied territory.
• Military occupation is period of "interim (political/legal) status." The occupied territory is said to be "in interim status status under the laws of occupation." Since the territory has not reached a final (political) status, it is a sub-sovereign entity.
• After war, in situations where a territory is separated from the "motherland" via the specifications of a peace treaty, the military government of the legal occupier does not end with the coming into force of that treaty. 
• The legal occupier may be described as "the principal occupying power," or alternatively as "the (principal) occupying power." This is because the law of agency is always available.  When the administrative authority for the military occupation of particular areas is delegated to other country’s troops, a "principal - agent" relationship is in effect.

Further Notes on Annexation

Annexation is when one country forcibly asserts control over another country’s territory and claims sovereignty. This usually follows the territory coming under the control of foreign military forces.

Annexation is unilateral and differs from cession. A treaty where it is specified that territorial title is being given, granted, transferred, sold, awarded, etc. completes the act of cession.

Importantly, international law does not recognize any transfer of sovereignty at surrender ceremonies.  Hence, an announced annexation of territory at the surrender ceremonies, or as a result of the surrender ceremonies, even if allegedly based on previous declarations, proclamations, etc. or other documents, is an illegal act.

Taiwan and the post-WWII Peace Treaty

Upon the coming into force of the San Francisco Peace Treaty on April 28, 1952, what is Taiwan’s legal status?

A popular theory in Taiwan says that with Japan renouncing its sovereignty over Taiwan, with no "receiving country" being specified, Taiwan has become terra nullius, and available for any interested country to annex. However, such a description of Taiwan was/is impossible, because terra nullius is spoken of unpopulated territory. In 1952, Taiwan had an estimated population of 8.25 million.

Therefore, it is incorrect to say that Taiwan became terra nullius, terra sine domino, derelict territory, or abandoned territory.  

In fact, Taiwan remained as territory under military occupation.