Simple English definitions for legal terms
Read a random definition: SIPA
An informal application is a patent application that does not meet the requirements set by the U.S. Patent and Trademark Office. This can include applications that are printed on both sides of the paper, not permanent, legible, or reproducible. However, an informal application can be corrected and still retain the original filing date.
For example, if an inventor submits an application that is not legible, they can correct the issue and still keep the original filing date. This means that they will not lose any time in the patent application process.