A temperature is an objective comparative measurement of hot or cold. It is measured by a thermometer. Several scales and units exist for measuring temperature, the most common being Celsius (denoted °C; formerly called centigrade), Fahrenheit (denoted °F), and, especially in science, Kelvin (denoted K). The coldest theoretical temperature is absolute zero, at which the thermal motion of atoms and molecules reaches its minimum – classically, this would be a state of motionlessness, but quantum uncertainty dictates that the particles still possess a finite zero-point energy. Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, and −459.67 °F on the Fahrenheit scale. Source:Wikipedia
The BBC have an interesting infographic about temperature.
Humidity is the amount of water vapor present in the air. Water vapor is the gaseous state of water and is invisible to the human eye. Humidity indicates the likelihood of precipitation, dew, or fog. Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. This effect is calculated in a heat index table or humidex. The amount of water vapor that is needed to achieve saturation increases as the temperature increases. As the temperature of a parcel of water becomes lower it will eventually not reach the point of saturation without adding or losing water mass. The differences in the amount of water vapor in a parcel of air can be quite large. For example, a parcel of air that is near saturation may contain 28 grams of water per cubic meter of air at 30 °C, but only 8 grams of water per cubic meter of air at 8 °C. There are three main measurements of humidity: absolute, relative and specific. Absolute humidity is the water content of air expressed in gram per cubic meter. Relative humidity, expressed as a percent, measures the current absolute humidity relative to the maximum (highest point) for that temperature. Specific humidity is the ratio of the mass of water vapor to the total mass of the moist air parcel. Source:Wikipedia
Dew point is the temperature to which air must be cooled to become saturated with water vapor. When further cooled, the airborne water vapor will condense to form liquid dew. When air with a high dew point contacts surfaces at colder temperatures, then liquid dew will form on the surfaces as condensation. Dew point is sometimes called frost point when the temperature is below freezing. The measurement of dew point is related to humidity. A higher dew point means there will be more moisture in the air. Source:Wikipedia