In Grasshopper, a specific location on the interior of a curve. Loci expand the concept of a curve parameter by allowing points on a curve to be specified in four different ways:

1. A numeric parameter on the curve domain.
2. A point coordinate in 3D space.
3. A normalised length along the curve.
4. An actual length along the curve.

When numbers or points are converted into loci, the results are loci of the first and second type respectively. Locus types two and three must be created with dedicated components.