I know this is an old thread, but there seems to be a lot of confusion surrounding region codes on PlayStation console. Hopefully this will clear things up.

First of all, the region map posted by another user is for DVD, not games. This map does not accurately reflect region coding of games and should not be referenced for this reason. For example, the map shows that AU and NZ share region codes with USA for DVD, however that is not the case for games. They usually share region codes with UK.

PS4 games are not region locked, so you can pick up a PS4 game intended for any other region and play it on your console. DLC on the other hand, is region locked. The region code of the DLC must match the region code of the game. The best way to avoid any problems accessing DLC is to buy the digital version of the game and DLC using the same PSN account, as there is no way to mess up.

If you prefer to buy discs, this information should help you find the right version:

CUSA, on its own, is not an indicator of the region the game is intended for. It does NOT mean it is for USA. CUSA is used for 3rd party (published by someone other than Sony) titles that are intended to be distributed in the Americas, Europe, and Australia/New Zealand. The number after CUSA indicates which region it is desginated for and varies by game, so unfortunately I can't provide a complete list. The region lock only affects access to DLC for the game. The easiest way to determine which CUSA code is for your region is to look up the digital version of the game on store.playstation.com. You will find the CUSA code in the URL for the game's store page.

Here is an example, with the CUSA code in red:
(USA) - https://store.playstation.com/#!/en-us/games/call-of-duty-black-ops-iii-gold-edition/cid=UP0002-CUSA02290_00-BLACKOPS3GOLD000
(Sweden) - https://store.playstation.com/#!/en-se/games/call-of-duty-black-ops-iii-gold-edition/cid=EP0002-CUSA02624_00-BLACKOPS3GOLD000
(UK) - https://store.playstation.com/#!/en-gb/games/call-of-duty-black-ops-iii-gold-edition/cid=EP0002-CUSA02624_00-BLACKOPS3GOLD000

As you can see, the CUSA codes for the USA version and the other two are different. However, the Swedish version and UK version are the same. Before you buy the game, look up the correct code for your account's region (sign in to your PSN account at store.playstation.com before searching for the game) and be sure to buy a game disc with that same code.

PLAS and PCAS codes are used for games publish by Sony. As with CUSA, PLAS and PCAS will be followed by a number which determines the region.

PlayStation 3 games use BLUS codes for the Americas, BLAS codes for parts of Asia, and BLES for most other regions. As with the PS4 region codes, the BLUS/BLAS/BLES will be followed by a number which indicates the region it is intended for. Thus, USA will have one BLUS code, whereas Argentina will have a different BLUS code. UK, Spain, France, Italy and Germany will have BLES codes, which may be the same or can be different. Australia and New Zealand will have the same BLES code as UK. As with the CUSA codes, you can find the BLUS/BLAS/BLES code for your region in the URL for the game's store page at store.playstation.com.

Some regions are not officially supported by game publishers, so you may need to create a PSN account for the region the game disc was imported from in order to buy and access DLC for the game. Brazil and India, as well as countries in Africa and the Middle East often fall into this scenario.