Protein requirement describes how much protein a person needs each day to maintain muscle, tissue and metabolic processes. How high this requirement is depends, among other things, on body weight, age, activity level and individual circumstances.
As a general guide, the German Nutrition Society (DGE) gives about 0.8 g of protein per kilogram of body weight per day for healthy adults, and from about age 65 a figure of about 1.0 g is often cited. In sports science, ranges of about 1.2 to 2.0 g per kilogram are often discussed for strength training or diet phases. This should be understood as a rough guide and not as a blanket recommendation from this site. People with kidney disease should generally have their protein intake clarified by a doctor.
The guide Calculating your protein requirement offers a calculation aid for your individual needs, the guide Protein in older age describes particularities in later life, and the guide Protein and kidney myths provides background on kidneys and protein.