Many patent applicants want protection not only in their country of origin, but also in other countries around the world.
Typically, in order to get worldwide protection, one would file a priority application and 12 months later one or more foreign applications. The foreign applications may claim priority from the priority application.
For example, you might a priority application in Singapore. 12 months later, you could file multiple separate foreign applications, e.g., in China, India, US, Europe, etc. But this process can be expensive because some countries will require you to file a translation of the patent specification into the local language. For example if you were to file a patent application in China, you would need to get the patent specification translated into the Chinese language. Similarly, the Japanese Patent Office will need you to file a patent specification in Japanese.
As an alternative to filing separate national applications, you can make use of the Patent Cooperation Treaty. Instead of filing multiple separate foreign applications as above, you file a single PCT application (also known as an International application). That PCT application can be treated as a “bundle” of national applications.
The PCT application will eventually need to be converted into separate national applications, but not until 30 months from the priority date (for some some countries the deadline is 31 months from the priority date).
Instead of you needing to make a decision about which of those countries to choose and which to discard at the 12 months stage, you can defer that decision to 30/31 months from the priority date. At the 30/31 month stage, you “nationalise” the PCT application in the countries of interest for you.
Hopefully, the additional 18 months will give you more time to make a better decision as to which countries these are, and also whether the invention can be effectively commercialised and to obtain further funding. You also get a search report and a non-binding examination report (Written Opinion) for the PCT application, which will give you a better idea of whether the invention is patentable or not.