boundary
dividing line between two areas or sets of points in a topological space; difference between the closure and the interior
delimiter
sequence of one or more characters used to specify the boundary between separate, independent regions in plain text or other data streams; one of various means to specify boundaries in a data stream
time horizon
fixed point of time in the future at which point certain processes will be evaluated or assumed to end
plate boundary
type of tectonic plate
Boolean domain
set consisting of exactly two elements, interpretable as false and true
nuclear drip line
boundary on a table of nuclides demarcating where atomic nuclei decay by emitting protons or neutrons
sphere
round, rotationally symmetric shape of the 2D surface of a ball in 3D space
snow line
point above which snow and ice cover the ground throughout the year