Copyright is a very important and sometimes unnoticed part of design. It is a tricky issue with a lot of grey area. Especially now with the web the way it is a sharing being such a huge part of the creative community.
Copyright is in place to create the work of inventors, artists, designers, poets, writers, brands etc. It 's goal is to stop people from directly copying the work of others and claiming it to be their own. This is of course bad would lead to chaos. You could copy someone's invention and sell it for yourself to get money that should be rightfully theirs. Or downloading someone's album and re-uploading it claiming it's all you and making money/gaining notoriety.
It is an essential pillar in the way that creative industries work. It ensures that your work is safe and that you get all the benefits and rewards you deserve from your work. However, it cannot control every use of your work as that would infringe on other (arguably more important) laws and principles. For example the principle of free speech. Something hugely important in western civilisation. Imagine quoting a film or singing a cover of a song and being sued by the creators for everything you own. The principles and rules that overcome this are called fair use. These are a series of scenarios and conditions wherein using someone else's work is acceptable and no action can be taken against them.
One of these principles mean that you are allowed to report on the work in question or create a review for example. You can show clips from a film or snippets of music from an album within a review and pass comment on the contents. You can give a summary of the plot and even reveal the whole storyline. This is allowed within the rules of copyright.
You are also allowed to create a parody of said piece. Taking the basic ideas and principles present, maybe even the script or original artwork. They make changes to make into something of your own. This is popular on the internet and also allowed within the rules of copyright.
One thing that is quite a contentious issue on the web, and in particular on YouTube, is the issue of using someone else's work but not for commercial gain. The main reason for copyright as I mentioned earlier is to stop others benefitting unfairly from other peoples creations. So if you upload a video you've created with someone else's music for the soundtrack and you put it up for monetisation and make a profit from it. It could be argued that the song had a say in that happening. This can lead to all of the audio being removed from your video or maybe even the video being taken down and restrictions being applied to the account.
You can get around this by uploading the video but revoking the monetisation options. This means there will be no adds displayed and no money made on your part. Some companies however, still take action against content creators who do that. This is unfair and not supported by copyright law. It is within the boundaries of fair use to upload someone else's work and have it not be for commercial gain on your part so long as you credit the initial creator of the work and state you do not own anything to do with it. If anything that is promotion for their work that is free however, some larger companies do not see it that way and have a rather outdated series of ideas about copyright and the Internet in general.
It is prevalent in design where brand identity is very important. Creating something unique that stands out is important and takes a lot of time, effort and resources. Copyright is there to protect any logos, slogans or jingles a brand may produce as that is tied into a product or company that would have certain values and ideals to uphold.
Copyright does however, have a time limit. It varies from country to country as to how long the copyright will last. This is a picture demonstrating those times and which countries they apply to:
After the time of publication, release or the copyright holder's death the clock starts ticking. Most countries average a time of around 70 years. This means that 70 years from the initial copyright the work will no longer be governed by copyright and will pass into the public domain. This means that it can be used freely by anyone and is not really technically owned by anyone.
There are a lot of talks constantly about the length of time and they are liable to change all the time. There are also issues with big companies owning individuals work and extending the copyright past reasonable points but they are discussions for another day.
For now I will leave you with a playlist of music that is now in the public domain and as a result completely free to enjoy and use!