# Glossary
Editor: words used in the editor and in this Help Center
Short meanings of the words in the editor. Each term links to its page.
| Term | Meaning |
|---|---|
| Absorber | A boundary that absorbs light slowly over many layers. More stable than PML, but needs more layers. |
| Bloch boundary | A periodic boundary that adds a phase shift. Use it for light at an angle on a periodic structure. |
| Boundary | What happens to light at the edges of the simulation domain. |
| Cross-Section | A 2D slice of the simulation on the canvas, for inspection. |
| Dispersive medium | A material whose properties change with the wavelength. |
| Domain | The box in space that the simulation covers. |
| Draft | A version that has not run. You can still change it. |
| EME | Eigenmode expansion. A project type for long waveguide devices. |
| Excitation Signal | The time shape of the light that a source sends, for example a Gaussian Pulse. |
| FDTD | Finite-difference time-domain. A project type that solves Maxwell's equations in time on a 3D grid. |
| Field decay | How fast the fields fade during an FDTD run. Results are reliable when the fields have faded. |
| Gaussian Pulse | A short pulse that covers a range of wavelengths. The default excitation signal. |
| Grid | The cells that the solver divides the domain into. A finer grid is more accurate and slower. |
| Heat | A project type for temperature and heat flow. |
| Medium | A material, of a structure or of the background. |
| Mode | A field pattern that travels along a waveguide without changing shape. Also a project type that computes these patterns. |
| Monitor | An object that records results in a region of the simulation. |
| Monitor Datasets | The group in the Results tab with the data that the monitors recorded. |
| Parameter | A named value that you can use in fields instead of a number. |
| PEC and PMC | Perfect electric and perfect magnetic conductor. Boundaries that reflect all light. |
| Periodic boundary | A boundary that repeats the simulation, so that one unit cell models an infinite array. |
| Permittivity | The material property that sets how light travels in it. The refractive index is its square root, for a lossless material. |
| PML | Perfectly matched layer. A boundary that absorbs light with almost no reflection. The default. |
| Run time | How long, in simulated time, an FDTD run lasts. |
| Script Object | Python code in the editor that creates structures, sources or monitors. |
| Shutoff | The field level at which an FDTD run stops early, because the fields have faded. |
| Source | An object that sends light into the simulation. |
| Structure | An object in the simulation: a geometry with a medium. |
| Symmetry | A setting that simulates only part of a symmetric setup, to save time and cost. |
| TFSF | Total-field scattered-field. A source that lights a box with a plane wave. Outside the box you see only the scattered light. |
| Version | A saved state of a project: v1, v2, and so on. A version that has run cannot change. |
| View Only | A project that you can see but not change, for example a project shared with you. |
Cloud only
| Term | Meaning |
|---|---|
| FlexCredit (FC) | The unit that a cloud run is charged in. |
| vGPU | A GPU that a license reserves on the cloud for your company. A run with vGPU costs no FlexCredits and waits in the company queue. |