The hour is a unit of time and is a multiple of an SI base unit with the symbol hr.
There are 60 seconds in a minute and 60 minutes in an hour. Consequently, there are 3600 seconds in an hour.
In a mean solar day, there are 24 hours.
Originally in the Middle East, the hour was defined as 1/12 of the day or night time. However, seasonal factors clearly affected all of these definitions and an average is used today to normalise and allow calculations.
The day is a unit of time and is an SI-derived unit with the symbol d.
On Earth, it is defined as 86,400 seconds and is approximately the time it takes for the earth to complete a full rotation around its axis. In the earlier days, this was measured by waiting for a cast shadow to match a template drawn from the previous day's shadow.
There are 365 days in a year and, on average, 30.42 days in a month.
The unit day has many different variants; depending on what is used to measure the Earth's rotation. In a sidereal day (a rotation with respect to a distant star or constellation, not the sun), there is actually 4 minutes less than 24 hours in a cycle.