**Core Concept**
Sleep apnea is a sleep disorder characterized by repeated episodes of partial or complete obstruction of the upper airway during sleep, leading to breathing pauses or apneas. These apneas can be central (from the brain), obstructive (from the airway), or mixed.

**Why the Correct Answer is Right**
The American Academy of Sleep Medicine defines sleep apnea as five or more episodes of apnea or hypopnea per hour of sleep. The correct answer, >30 apnoeas during 7 hours of sleep, equates to approximately 4.3 apnoeas per hour, which meets the criteria. This definition is crucial for diagnosing and managing sleep apnea, a condition that affects millions worldwide and is linked to various comorbidities, including hypertension, diabetes, and cardiovascular disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option underestimates the number of apnoeas required for a diagnosis of sleep apnea.
**Option C:** This option specifies a shorter duration of sleep and an incorrect threshold for apnoeas.

**Clinical Pearl / High-Yield Fact**
The Epworth Sleepiness Scale (ESS) is a widely used questionnaire to assess daytime sleepiness in patients with sleep apnea. A score of 10 or higher indicates excessive daytime sleepiness, which can impact daily functioning and quality of life.

**✓ Correct Answer: B. >30 apnoeas during 7 hours of sleep**