1. The terms $I_{xx}$ and $I_{yyy}$ typically refer to moments of inertia in physics and engineering. 2. $I_{xx}$ is the moment of inertia about the x-axis, which measures how mass is distributed relative to that axis. 3. $I_{yyy}$ is less common notation, but it might be a typo or refer to a higher order moment or a moment about the y-axis, often written as $I_{yy}$. 4. The moment of inertia $I_{xx}$ is calculated as $$I_{xx} = \int (y^2 + z^2) dm$$ where $dm$ is a mass element and $y,z$ are coordinates perpendicular to the x-axis. 5. Similarly, $I_{yy}$ is $$I_{yy} = \int (x^2 + z^2) dm$$ measuring distribution about the y-axis. 6. These quantities are important in rotational dynamics to determine resistance to angular acceleration. 7. If you meant something else by $I_{yyy}$, please clarify.