The sound a cat makes when it wants attention, as opposed to 'meow', 'rrow', or 'mow'.
More often than not a cat will repeat 'meh' several times in a row to attract attention to themselves.
(Kiki is walking by Billy the cat and standing next to her food and water bowls.)
Billy: Meh, meh, meh, meehhhhhh, mehhhhhhhhhh!!!
Kiki: Billy wants meh?