Merge pull request #364 from jni/define-segmentation

Define segmentation when it is first mentioned

Author: K-Meech

episodes/07-thresholding.md

@@ -26,7 +26,9 @@ exercises: 50
 In this episode, we will learn how to use scikit-image functions to apply
 thresholding to an image.
 Thresholding is a type of *image segmentation*,
-where we change the pixels of an image to make the image easier to analyze.
+where an image is split into different regions, or *segments*.
+These segments can then be analyzed separately.
+
 In thresholding, we convert an image from colour or grayscale into
 a *binary image*, i.e., one that is simply black and white.
 Most frequently,