A loose leaf is a piece of paper that is not bound in place, or available on a continuous roll, but typically punched so as to be organized in a ring binder. Loose leaves may be sold as free sheets, or made up into notepads, where perforations allow them to be removed easily. "Leaf" in many languages refers to a sheet or page of paper, as in Folio, as in feuille de papier (French), hoja de papel (Spanish), foglio di carta (Italian).
"Loose leaf" describes any kind of paper or book that is available in single sheets, unbound. Its "leaves", or sheets, are "loose" and not bound in notebook or book form. However, it seems "loose leaf" in the USA (and this entry) refers most specifically to a lined and punched paper, or ruled paper, a school supply also known as "binder paper" that can be sorted in a loose leaf binder. This may be a typical 3 ring binder but "loose leaves" of other types can also go in a date book, address book or artist's portfolio, additionally there are also loose leaf textbooks.
There are three common types of binder paper: wide ruled, college ruled, and unruled. College ruled paper has less space between the blue lines, allowing for more rows of writing. Wide ruled paper is intended for use by grade school children and those with larger handwriting.
The chief advantage of loose-leaf paper is its flexibility and economy in use. A punched sheet of paper can be inserted into a ring binder, removed for separate use, and then returned to the binder. Different sheets can be organized into a different order in a binder, or removed entirely and refiled in another binder, or disposed of as needed. This ability to rearrange and update the contents of binders is convenient for students and others, who can carry only the papers they are likely to need on a given day, while leaving the remainder elsewhere. The ability to add or remove an arbitrary number of pages has been useful for reference works that are frequently updated, such as computer software manuals, parts catalogs, and legal indexes. Or it need not be bound at all and can stand on its own as a single paper.
The chief disadvantage of loose-leaf paper is that individual pages can be easily removed or lost from its storage binder due to tearing or wear of the punched holes. Adhesive reinforcement labels or sheet protectors are available to make pages more durable, and ring binders are often equipped with sheet lifters or other features to reduce wear and damage to their paper contents. Ring binders are sometimes banned from use for written journals, logs, or registers, which may even have pre-numbered permanently bound pages to discourage removal of pages, or at least allow a removal to be detected.