When you receive your book contract, 99.9% of the time you will see a "grant of rights" section. What does that mean? Do you own your book if you grant the publisher this right?
Under Section 106 of the US Copyright Act of 1976, authors are granted a bundle of rights:
The right to reproduce the copyrighted work.
The right to prepare derivative works based upon the work.
The right to distribute copies of the work to the public.
The right to publicly perform the copyrighted work.
The right to publicly display the copyrighted work.
The right to perform the copyrighted work publicly by means of a digital audio transmission (for sound recordings)
This essentially means that as the copyright owner of your book, you can transfer the rights listed above to others individually (for example, just the distribution right) or as a group (everyone of the rights). So how can you transfer these rights? You can grant them or assign them.
Grant of Rights vs. Assignments
If you grant a right, you are essentially transferring that right to someone else, but you still own the right. You are merely allowing someone to, for example, reproduce your work or distribute your work. You can do this exclusively or non-exclusively. For example, you can allow just one publisher to publish your audiobook (exclusive) or allow multiple publishers to publish your audiobook (non-exclusive). In this scenario, you'd likely only transfer the publication right exclusively since most publishers won't want competition (but you get the picture). You can also further subdivide your grant to only allow publication in certain languages in certain territories (for example, you license an audiobook to be published in the English language only in North America).
If you assign a right, you forego copyright ownership of that right. So if you assign your reproduction right (or any other right mentioned above for that matter) to your publisher, you no longer have control of it. You may ask why would anyone do this? Well, some authors (like professors trying to obtain tenure, for example) may not care about relinquishing ownership because they only care that are being published by a prestigious academic press.
I hope this mini introduction has helped. Do you have a book contract and need assistance reviewing it? Don't hesitate to reach out to Perry Law.