Glossary
What do book app terms like DRM, credits and holds mean?
Most confusion about reading apps comes from a few words that sound simple and hide the terms of the deal: a credit is not a book, a borrow is not a purchase, and DRM decides whether you can take your books elsewhere. This glossary defines 34 terms in plain English, with a link to where each one matters on this site.
Why does a glossary matter for choosing an app?
The words on a pricing page are where the real terms live. "Included" usually means rented. "Credit" means a token you can trade for one book, which may expire. "Listen while subscribed" means the book locks when you stop paying. Reading those words carefully is the difference between building a library and renting one.
Every definition below is written for a reader, not a publisher, and stays close to how the companies themselves use the term. Where a term belongs to one company, we say so.
How should you use this page?
Search it with your browser's find command, or read the four groups in order: formats and files, buying and borrowing, features, and recaps and AI. Each term links to a review or guide where it decides something.
Formats and files
- EPUB
- The open standard ebook format used by most stores and readers except Amazon's. An EPUB without DRM opens in almost any reading app. Where it matters
- KFX and AZW3
- Amazon's Kindle ebook formats. Kindle store books arrive in these formats, almost always with DRM, and open only in Kindle apps and devices. Where it matters
- A fixed-layout document format. Fine for manuals and papers, awkward on a phone because text does not reflow. Where it matters
- MP3 and M4B
- Common audiobook file formats. M4B keeps chapters and your place in one file. Libro.fm sells DRM-free audiobooks you can download in these formats. Where it matters
- DRM
- Digital rights management: copy protection that ties a book to one company's apps and devices. DRM is why most store purchases cannot move to another app. Where it matters
- DRM-free
- A file without copy protection. You can back it up and open it in any compatible app, which is the closest thing to owning a digital book. Where it matters
- Sideloading
- Adding a file you got elsewhere (for example a DRM-free EPUB) to a reading app or e-reader yourself, rather than buying it in that app's store. Where it matters
- Send to Kindle
- Amazon's service for sending your own documents and compatible ebook files to a Kindle library by email, app or browser. Where it matters
Buying and borrowing
- Credit
- A token, usually one a month, that you trade for one audiobook regardless of its price. Audible Premium and Libro.fm use credits. Audible Premium credits expire 12 months after issue or when you cancel. Where it matters
- Selection (Audible Standard)
- Audible Standard's monthly pick. Unlike a credit, a selection plays only while you remain a member and does not roll over. Where it matters
- Included catalog
- A rotating set of titles you can read or listen to as part of a subscription, such as Audible's Plus catalog. You lose access when you cancel or when a title leaves the catalog. Where it matters
- Buffet subscription
- Our shorthand for all-you-can-read plans such as Kindle+, Kobo Plus and Everand: one monthly fee, a rental catalog, nothing kept. Where it matters
- Kindle+
- Amazon's borrowing subscription, called Kindle Unlimited until 22 October 2026. $11.99 a month in the US, up to 20 titles at a time. Where it matters
- Borrow limit
- How many titles a subscription or library lets you hold at once. Kindle+ allows 20, magazines included. Where it matters
- Hold
- A place in the queue for a library ebook or audiobook that is out on loan. Libby notifies you when it is your turn. Where it matters
- Loan period
- How long a library borrow lasts before it returns itself, commonly one to three weeks depending on your library. Where it matters
- Monthly borrow cap
- Hoopla's model: no holds, but your library sets how many titles you can borrow each month. Where it matters
- Listening hours
- Spotify's model: a monthly allowance of audiobook time (15 hours on US Premium Individual) counted at normal speed and expiring each month. Where it matters
- Top-up
- A one-time purchase of extra Spotify audiobook hours, valid for 12 months but inaccessible while you are not subscribed. Where it matters
- À la carte
- Buying one book at a time at its listed price, without a subscription. Where it matters
- Lock-in
- Everything that makes leaving an app costly: DRM, missing export paths, rented catalogs. Every review on this site prints a lock-in table. Where it matters
Features
- Whispersync
- Amazon's sync between devices and between a Kindle ebook and its Audible narration, so you keep your place when you switch. Where it matters
- Immersion Reading
- Reading the text with the matching narration playing and words highlighted. Amazon offers it for owned Kindle and Audible pairs, and Audible added it to its own app in February 2026. Where it matters
- Page Match
- A Spotify feature that moves you between a print or ebook copy and its audiobook at the same point; since October 2026 it accepts page numbers after an ISBN scan. Where it matters
- X-Ray
- A Kindle feature that lists characters, terms and places in a book, with where they appear. Where it matters
- Export
- Getting your data out: a CSV of your reading history, a file of your highlights, or the book files themselves. The single best test of whether an app respects you. Where it matters
- Reading tracker
- An app that logs what you read and how far you got, such as StoryGraph, Goodreads or Hardcover. Where it matters
- TBR
- To be read: your list of books you intend to read next. Where it matters
Recaps and AI
- Book recap
- A refresher of a book you are reading, usually fiction, that stops at your place. Different from a summary. Where it matters
- Book summary
- A condensed version of a book you have not read, usually nonfiction, ending included. Blinkist and Shortform sell summaries. Where it matters
- Recaps (Kindle)
- Amazon's "Previously on" style refreshers for earlier books in a series you have read, announced 2 April 2025 for Kindle ebooks in the US. Where it matters
- Story So Far
- Kindle's spoiler-free recap of the current book up to where you stopped, for thousands of popular fiction titles, on Kindle devices and the Kindle iOS app in the US. Where it matters
- Ask this Book
- A Kindle feature that answers questions about plot, characters and themes without spoilers, launched on the Kindle iOS app in the US in December 2025. Where it matters
- Page-locked recap
- A recap, cast list or answer limited to what you have read so far. Magic Bookmark does this from a photo of your page, a page number or the last line you heard, for supported titles on iPhone. Where it matters
Questions readers actually ask
- What does DRM-free mean for ebooks?
- The file has no copy protection, so you can back it up and read it in any app that supports the format.
- Is an Audible credit the same as a book?
- No. A credit is a token you trade for one book. Premium credits expire 12 months after issue or when you cancel, so an unspent credit can be lost.
- What is the difference between a recap and a summary?
- A recap refreshes a book you are reading and stops at your place. A summary condenses a book you have not read, ending included.