The question about the definition for global warming or in other words "what is global warming" is relatively easy to answer. We hereby lean at the definitions and explanations given in Wikipedia:
Global warming is the observed and projected increases in the average temperature of Earth's atmosphere and oceans. The Earth's average temperature rose about 0.6° Celsius (1.1° Fahrenheit) in the 20th century, see temperature graphs below.
Fig. 1: Definition for global warming: Temp. increase in the last 1'000 years (graph from http://www.globalwarmingart.com/images/b/bb/1000_Year_Temperature_Comparison.png)
Fig. 2: Definition for global warming: Temp. increase in the last 150 years (graph from http://www.globalwarmingart.com/wiki/Image:Instrumental_Temperature_Record_png)
According to different assumption about the future behaviour of mankind, a projection of current trends as represented by a number of different scenarios gives temperature increases of about 3° to 5° C (5° to 9° Fahrenheit) by the year 2100 or soon afterwards. A 3°C or 5° Fahrenheit rise would likely raise sea levels by about 25 meters (about 82 feet).
Fig 4: Definition for global warming: Temp. increase until the year 2100 (graph from http://www.globalwarmingart.com/wiki/Image:Global_Warming_Predictions_png.