Bowel activity is variable and can be significantly influenced by diet and hydration, but most people open their bowels (also known as pooing, crapping, bowel movement/evacuation) somewhere between three times a day and three times a week, with little need to strain and generally formed stools (poo, faeces, motions).
There is no commonly accepted definition of diarrhoea but it is generally understood to be a condition of loose, watery stools, with or without a frequent need to have a bowel movement.
There are many different potential causes but the three most common are motility disturbance (irritable bowel syndrome), infection and inflammation.
Most acute episodes, which resolve within a week or so are due to infection and do not require further investigation. However, if symptoms persist, and particularly if accompanied by certain other symptoms (e.g. rectal bleeding, weight loss, waking in the night with need to open bowels), it is important to seek medical advice.
Depending on the pattern of symptoms, there may be a number of different investigations recommended, varying from blood and stool samples, to scans and colonoscopy.