Adventitious: Structures or organs developing in an unusual position, as roots originating on the stem.*
This Crassula ovata (jade plant) is producing adventitious roots along its stem. This may be an indication that the plant is pot-bound and is trying to get roots into new soil.
*Harris, J.G., Harris, M.W. (2001). Plant identification terminology: An illustrated glossary (2nd ed.). Spring Lake: Spring Lake Publishing.