I have been going through this paper: Seam Carving for Content-Aware Image Resizing which talks about resizing images by seam carving depending on the image energy or the energy function.
Some related quotes from the paper are:
A seam is a connected path of low energy pixels in an image
A seam is an optimal 8-connected path of pixels on a single image from top to bottom, or left to right, where optimality is defined by an image energy function
So, what does the 'energy' in an image mean, in this particular context?