Key words for Population.

Habitat: the place where an organism normally lives, which is characterised by physical conditions and the species of other organisms present.
Random Sampling: it's used to avoid any bias in collecting data.
Systemic Sampling: samples are taken at regular intervals within a set sampling area.
Abundance: counting the number of individuals of a species in a given space.
Frequency: it's the likelihood of a particular species occurring in a quadrat.
Percentage cover: is an estimate of the area within a quadrat that a particular plant species covers.
Mark-release-recapture: known number animals caught, marked and released.