The question is asking about the nature of Celsius temperature.

Option 1: Relative temperature. This means that the Celsius temperature is measured in relation to other temperatures. For example, we compare the Celsius temperature of one day to the Celsius temperature of another day to determine if it is hotter or colder.

Option 2: Absolute temperature. This would mean that the Celsius temperature is measured independently and does not rely on any other temperature scale. However, this is not true for Celsius, as it is based on the Celsius scale which is derived from the Kelvin scale.

Option 3: Specific temperature. This refers to a particular temperature value or measurement. While Celsius temperature itself represents a specific value, this option is not the best description for Celsius as it does not encompass its relative nature.

Option 4: Approximate temperature. This means that the Celsius temperature is an estimation or approximation rather than an exact measurement. However, Celsius temperature can be precisely measured using a thermometer, so this option is not accurate.

Therefore, the correct answer is option 1, relative temperature.