The word blanch refers to a cooking technique in which food is briefly immersed in boiling water or fat.
Blanching vegetables softens them just enough so that they can then be quickly cooked over high heat, such as in a stir fry, where a short time in the pan wouldn't be enough to soften them, but cooking them longer would tend to overcook the other items in the pan.
Blanching is also a good technique to use for vegetables that will be featured in salads, so that they're softened just enough so that you can eat them more or less raw, but they won't be excessively difficult to chew. Think carrots or broccoli here.