Definition:
Noun: A mode of wireless communications that allows two or more devices to exchange information over the Internet. The device must be within range of a wireless access point (WAP), like a router connected to the Internet, to use Infrastructure mode.
In the PSP's case, different games support different kinds of interactions over Infrastructure mode. Some will allow you to play the game with other PSP owners worldwide. Other games allow you to download content that another user has created, like a new map, and submit your own creations. Another possibility is that you can submit your high scores for a game to the worldwide rankings.
You can see whether a game supports Infrastructure mode by looking for a text box saying “Wi-Fi Compatible (Infrastructure)” on the back of the game's packaging.
Pronunciation: IN-fra-struk-shur
Also known as: Online play, Internet play
Examples:
You can compete with gamers from around the world over Infrastructure mode.
For Infrastructure play, you will need to connect your PSP to the Internet.