A projector's native resolution is the number of pixels the projector uses to create the image. The more pixels it uses, the higher the resolution.
How much resolution do I need?
High-resolution projectors are able to show more complex picture detail than low resolution projectors. In addition to giving you more acute image detail, since there are more pixels used to make the image, each individual pixel is smaller, so the pixels themselves become less visible on the screen. However, you will generally pay more for higher resolution.
Lower resolution projectors are much less expensive, but they can produce images that are just as bright and attractive as higher resolution machines. Unless you have a specific need to display complex images with a lot of fine detail, buying a lower resolution projector will be your best bet from a cost perspective.
Xga (1024x768) - XGA resolution has been around since the 1990's, but it is still a highly popular format that a lot of folks are buying. Unlike wuxga & wxga, xga is a 4:3 aspect ratio, so it has the format of the older CRT-type TV picture rather than the modern widescreen formats. Xga resolution is inexpensive which contributes to its continuing popularity. However, there are also many large venue XGA projectors on the market that are ideal for signage and other applications where widescreen format is not desirable or appropriate and higher resolution is not necessary. Think about the display of lyrics to guide the singing of hymns in a house of worship for example, the text is very large so high resolution is irrelevant.
Wxga (1280x800) - wxga projectors have widescreen 16:10 aspect ratio. The very bright 1280x800 models can be ideal in large scale digital signage applications where brightness is king, and the subject matter being displayed does not demand high resolution presentation.
Wuxga (1920x1200) - wuxga is a widescreen, 16:10 aspect ratio format that is highly popular in commercial and business use today. wuxga projectors have the advantage of being able to natively display 1080p HD signals as well as 1920x1200 content,, making it a go-to resolution for both business presentation and video applications.
HD (1920x1080) - is full HD 1080p and 16:9 format. This of course is the most popular resolution for home theatre projectors but can also be used for business use.