It seems like a strange word, but it means to "make your pattern true", or to ensure that it is accurate, correct and complete.
It's a step that is all too often overlooked, but taking the time to properly complete your paper pattern is essential to make the sewing process much, much easier
In this video, I explain the "language" of patterns, where to place notches, and how to add seam allowance to your final pattern.
Notches and markings on your pattern tell you (or anyone else using the pattern) how it goes together.
The single and double notches on the cap of the sleeve, for example, match the single and double notches in the armhole - AND indicate which side of the sleeve is the front and which is the back.
That's what I mean by the "language" of patterns.
You can get more information about truing your patterns - including another video and information on how to add simple facings - on the following page:
Please don't neglect this important step when making your patterns!