Data Compression

Reducing the 'electronic space' (data bits) used in representing a piece of information, by eliminating the repetition of identical sets of data bits (redundancy) in an audio/video, graphic, or text data file. White spaces in text and graphics, large blocks of the same color in pictures, or other continuously recurring data, is reduced or eliminated by coding (encryption) with a program that uses a particular type of compression algorithm. The same program is used to decompress (decrypt) the data so that it can be heard, read, or seen as the original data. Compression ratios of 1:10 to 1:20 (or much higher, with emerging technologies) are routinely achieved with common types of data, resulting in much smaller storage space requirements or much faster communications. Fax machines were the earliest consumer equipment to use a data compression technology. Also called data compaction. See also streaming media (businessdictionary.com).

The most widely used is ZIP on the PC. It is NOT the best as others have said. It's been around the longest. However it does not compress as well as RAR AND, most importantly, is not 100% foolproof. It can and often does inject errors into the zip file. However if you are planning on using file compression on your documents and files and will be distributing them around to various people then your best choice is ZIP because of it's availability to the receivers. If this is for personal use RAR is better. ZIP and RAR are just some of the common data compression apps. '-'