A population is a group of individuals of a single species that live in a particular area and interact with one another1. These interactions include sexual reproduction and competition for common resources.
An example of a population would be the Emerald Ash Borer in Southern Arkansas. These beetles are all members of the species (Agrilus planipennis), reproduce together, and compete against each other. They also are physically separated from other populations of emerald ash borers by distance.
Populations are limited by habitat suitability, abiotic and biotic factors within the environment, and species dispersal1. A new population of a species cannot form in an area that they cannot access or is unsuitable for them. Populations are also dynamic; the size of a population changes over time and location due to a variety of factors such as food availability or disturbances.
1. Cain, M. 2014. Ecology. Sunderland, MA: Sinauer Associates