With this new feature, livestreamers on Meerkat can tap on one of their viewers’ profiles and invite them to do a “cameo” within their original stream. That viewer can then basically take over the stream for up to 60 seconds (either user can end the cameo at any time before this), after which the cameo ends and the feed reverts back to the original livestream.
Source: Meerkat adds new ‘takeover’ feature, Cameo, to live-streaming app – FierceOnlineVideo