According to Institute of Medicine, safety is defined as “freedom of accidental injury”.

Reference:

Emanuel, L., Berwick, D., Conway, J., Combes, J., Hatlie, M., Leape, L., Reason, J., Schyve, P., Vincent, C., & Walton, M. (2008). What exactly is patient safety? Advances in Patient Safety, Vol. 1: Assessment. Retrieved from http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=aps2v1&part=advances-emanuel-berwick_110