Periodicity and quasiperiodicity

Periodicty is the quality or state of being periodic, recurring at regular interval.

In mathematics a periodic function is a function that repeats its values in regular intervals. Examples are sinus, cosinus and tanget functions.

In physics periodic functions describe phenomena such as oscillations and waves.

Some systems display a pattern of recurrence with a component of unpredictability. The term quasiperiodicity can be used to describe the such a system.

In physiology/medicine the healthy heart rhythm (sinus rhythm), as measured by an ECG, is characterized by periodicity.

Heart rhythm disorders can be characterized by quasiperiodicity.

Sources: http://www.emedicinehealth.com/heart_rhythm_disorders/article_em.htm http://www.memidex.com/periodicity http://www.ncbi.nlm.nih.gov/pmc/articles/PMC507798/ http://www.thefreedictionary.com/periodicity