Public domain

Being in the public domain refers to any original material that is not copyrighted (either because it never was, or the copyright has expired) and is not owned by anyone. This material, be it music, photographs, video, computer code, or literature can be used, copied, and distributed by anyone without restriction.

Freeware

Freeware generally refers to games or software applications that can be used, downloaded, and distributed free of charge but differ from material in the public domain in that it is still owned and copyrighted by its developer.

It is usually distributed under license that prohibits reselling, modification, or its incorporation into anything you may be developing yourself and may also limit its usage by businesses or for business purposes.

Shareware

Shareware is more commonly associated with software applications that you can get as a free download on a trial basis, knowing that you will have to pay for the complete version should you like it. You will usually find that the developer has incorporated an expiration date or disabled some of the more important functions as an incentive to upgrade. Such restrictions are then removed once the full version has been purchased.

Abandonware

Abandonware describes software (usually old games) that are no longer sold or supported by their original developer. Distribution is maintained by enthusiast websites which can offer them for download, but as with freeware, cannot sell or alter the product.

Game demos

Another type of free download readily available is the game demo. They are usually playable, but stripped down versions of the full game with limits on gameplay and access to features.

Game demos are typically released by the publisher for consumers to try them out and decide whether or not to buy the full version.

Streaming

Quite often, a website will offer music or video streaming. This is unlike the other methods in that the user doesn't download the file, but views or listens to it online.

Streamed material however, is not intended to be saved to your computer and will most likely have copyright protection. You should also check the site's license agreements and usage policies regarding the material you have access to if you are thinking of recording any steamed media.

Royalty-free

Royalty-free does not mean, as the title might suggest, that the material is actually free. The user will typically have to pay a 'one time fee' which will allow them to use it for profitable purposes (such as part of a commercial) as many times as they want without the need to pay any subsequent royalties. This material can be anything from music tracks to sound effects or pictures, and there are generally no restrictions on the number of times the material can be used.

There aren't usually any renewal fees, but restrictions will include the re-selling or lending of the material to anyone who has not purchased the licence.