Human resources is a term used to describe the individuals who comprise the workforce of an organization, although it is also applied in labor economics to, for example, business sectors or even whole nations. Human resources is also the name of the function within an organization charged with the overall responsibility for implementing strategies and policies relating to the management of individuals (i.e. the human resources). This function title is often abbreviated to the initials 'HR'.
Human resources is a relatively modern management term, coined in the 1960s. The origins of the function arose in organizations that introduced 'welfare management' practices and also in those that adopted the principles of 'scientific management'. From these terms emerged a largely administrative management activity, co-ordinating a range of worker related processes and becoming known, in time as the 'personnel function'. Human resources progressively became the more usual name for this function, in the first instance in the United States as well as multinational corporations, reflecting the adoption of a more quantitative as well as strategic approach to workforce management, demanded by corporate management and the greater competitiveness for limited and highly skilled workers.
Personally, I hate the term but it is in such common use that I cannot totally avoid it.