Someone who constantly says things, but never demonstrates they mean it with their actions. They can easily convince other people based on their words alone. They are manipulative. In many situations, their actions go against the words they have said, but since they are so good at getting around things with their words, they can talk their way out of it. They are very shallow. They cannot be trusted and lead deceptive lives. Their words and actions never line up with each other.
That girl sure is a talker; she never does anything to back up her words.
He is a talker; always telling you things, without proving he means them.