In the context of sampling natural populations, a line drawn across the region of interest. Sampling may consist of examining the occurrence of organisms along the line, or visible from the line, or within a sequence of quadrats centred on the line.
Biology
A straight line across an expanse of ground along which ecological measurements are taken, continuously or at regular intervals. Thus an ecologist wishing to study the numbers and types of organisms at different distances above the low-tide line might sample at five-metre intervals along a number of transects perpendicular to the shore.