A carrier oil is also known as a base oil and it is used to dilute essential oil for massage. Essential oil is too strong to be applied directly to the skin, so a carrier oil is used for safety.
A carrier oil is a mild oil that contains little to no scent and does not evaporate unlike essential oils. Olive, almond, avocado, sesame, sunflower, grapeseed and primrose are all examples of carrier oils. Massages can require either light or heavy oil and carrier oils are chosen for their individual viscosities. Grapeseed is considered a very thin oil while olive is quite heavy.