Final answer:
The letter 'h' in this context stands for 'hour' which is a unit of time measuring duration. It is commonly used to calculate daily energy needs or measure sleep duration.
Step-by-step explanation:
'h' in this context stands for 'hour'. It is a unit of time that represents 60 minutes or 3,600 seconds. It is commonly used to measure duration or time intervals, for example, in calculating daily energy needs or recording sleep duration.'