Question: What does it mean if a file is zipped?
Answer: A zipped file is one that has been compressed. The size of the file is most likely much smaller than the original size (may be as little as half). Zipping files compresses them by removing redundant data from them - eg indicating that a given character is repeated twenty times may only take up two or three bytes instead of twenty. Zip files are created using a standard compression algorithm and so are readable by a variety of different compression programs (winzip is the most popular).
Zipping files makes them smaller and therefore quicker to send via email or to download from the internet. When a zipped file is received it must then be unzipped to restore the original code in order for it to be used.
It is also possible to create a zip archive where one zipped file contains the compressed copies of a number of files. When unzipped this will recreate all of the files that were contained within it. This makes the format useful for sending a group of files that belong together.
Recent versions of Windows can handle zipped files without needing a separate program to process them. Simply right click on the zip file and select "Extract All" from the context menu to create a decompressed copy of the zip file. While Windows also allows you to access the content of the zip file as if it were a folder, you should not access files that way other than to copy the individual files out if the zip file. Most likely the program you want to use the file with will be unable to process the file if it is still inside the zip file.
Linux splits the compression and archiving functions of a zip file into two separate processes. A Linux "tar" file is an individual file that has been compressed. Multiple files can be combined together into one "gz" or "gzip" file. Linux also supports the "zip" format.
This article written by Stephen Chapman, Felgall Pty Ltd.