Experiments or measurements often generate large sets of numbers on a grid. Tables of numbers are difficult to interpret, so we turn them into visual images in an attempt to make some sense of the data. At the simplest level a digital image is just an array of data. Each datum in an image, called a pixel, represents a color.
How do we assign colors to the data? For temperature it might seem logical to let blue represent cold, green intermediate, and red hot, but any scheme could be used. Usually color is chosen to make the image easy to interpret. A scale or legend by the figure defines the meaning of the colors. Depending on the circumstances, the colors may look real; that is, they may look like we imagine the scene appears to the eye. False color results when some other scheme than natural color is used for displaying images.
The term "false color" does not mean that the data are wrong or that the picture is deceiving you. It only means, don't be deceived; this figure is not a color photograph. You should look at the scale or legend to interpret it.