Emotional or psychological backing, as opposed to material help. For example, There's not much I can do at the doctor's office, but I'll come with you to give you moral support. [Late 1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.