rigid-widthregion
nounUK /ˈrɪdʒ.ɪd ˈwɪdθ ˌriː.dʒən/
US /ˈrɪdʒ.ɪd ˈwɪdθ ˌriː.dʒən/
A part of a computer screen that always stays the same size and cannot get wider or narrower.
The sidebar is a rigid-widthregion, so it never changes size when you resize the window.
OTHER MEANINGS
2. A section of a printed page whose width is set and cannot be changed.
The table sits in a rigid-widthregion at the top of the form.
3. A part of a design template that keeps a locked width while other parts stretch.
In the template, the logo bar is a rigid-widthregion.
4. A block in a user interface that ignores resizing and keeps its original width.
The toolbar is a rigid-widthregion, so it stays the same on every screen.