According to the deplorable E! channel special* "Hollywood's 25 hottest cougar tales" which I appear unable to wrest myself away from, a couple in which the female partner (or cougar) is significantly older than the male ** (cub).
Regional variant, courtesy of Naomi Watts: the Australian version of cougar is dingo (etymology - "the dingo ate my baby")
*: My shameful secret - I am a complete sucker for this particular brand of cultural detritus. Any VH1 or E! channel special involving lists or countdowns will keep me slackjawed before the TV. Can you say "Top 20 weird celebrity baby names", Jermajesty Jackson?
**: female cubs are also a possibility, e.g. Ellen deGeneres and Portia Rossi.